so, im due to start a strahd campaign soon, i have chosen to play a grave cleric in service to the raven queen. my concept was for him to act as a traveling acolyte who offers funeral rites and other services around laying dead to rest and helping the grieving process along with healing those whose time has not come. he also must root out undead and should he find them, destroy them, as the raven queen specifically despises intelligent undead (unless they are in service to her). 

now to the point, ive learned that one of the part is playing a necromance, not a huge issue, he can turn a blind eye to them raising undead puppets as long as there not doing objectively evil things or planning to become a lich or vampire, however a different character is playing a revenant, one who actively chose to become one and has no unfinished business to complete, this is the problem, by my characters faith he should destroy them, this obviously isn't an option.

so i have two choices left, completely ignore my characters religion and continue, the dm already told me he wont take my powers away but that feels wrong.

alternatively, I could refuse aid to the undead, siting that though we have bigger problems I still feel using my powers to help them would be a serious breach in my faith.

I'm open to the roleplay and difficult moments of this strained dynamic but I still feel like this will cause problems at the table.

My question is, how much should I let this influence my character?

Personally, i would oppose this and stand against undeads whenever possible. Mainly because Grave Cleric of the Raven Queen are intolerant of them; 

"Grave Cleric are followers of deities that seek to put restless spirits to rest, destroy the undead wherever they find them. They have the ability to sense the presence of the undead, whose existence is an insult to the natural cycle of life".

"The Raven Queen’s followers are expected to serve her will in the world. She concerns herself with ensuring that those fated to die pass from the world as expected, and bids her agents to defeat those who seek to cheat death through undeath or other imitations of immortality. She hates intelligent undead and expects her followers to strike them down, whereas mindless undead such as skeletons and zombies are little more than stumbling automatons in her eyes"

EDIT For Revenant party-member though things would be a little bit more complex, perhaps it would be trying to help understand the reason behind this spirit restlessness to eventually find out what can ease its suffering and finally help put it to rest;

"Followers of these deities seek to put restless spirits to rest, destroy the undead wherever they find them, and ease the suffering of dying creatures."

Sounds like a fun source of tension! 

Your cleric could see this as an important learning opportunity. If a revenant can come back without unfinished business, this is something worth observing and noting for the entire priesthood of the Raven Queen. And you can keep pushing their character to see if they really do have unfinished business they are hiding. 

You could also take the "caring priest" role, trying to convince them to let you resurrect them to live out the normal span of their life. 

Then you can revisit the dilemma as roleplay scenario if you feel there is nothing more to investigate and no chance of them willingly passing on. I would talk to the DM about how far on you can push that dilemma into the campaign, or if its something that will cut short your character's run earlier than you'd like. 

When the dilemma comes to a head, you still have options.

There is always the possibility of calling out the revenant to a fight to the death, or ambushing them, or trapping them somewhere to willingly pass on.

If your party is against pvp altogether, maybe you can also use it as a chance to swap in a new character or adjust your cleric's subclass to something like a death cleric. It could be a fun character arc, or even a reason to pass off your cleric to the DM to become a future antagonist. 

A more radical change would be if your cleric can't bring themselves to strike down their comrade and lose their divine connection entirely. You could work with your DM about switching your class altogether, basically making a new character sheet for the same person going forward. 

I have a similar situation. A fellow player died in the game and the DM brought him back by my god (of Death) as a Reborn because "it was not yet his time." The way I played it was my Grave cleric saw this as proof of his faith and saw him as a reborn chosen one of the faith and vowed to follow and protect him. An apostle of sorts. Creating a bond between our two characters, for better or worse. Also, throughout the campaign, we had encountered intelligent good undead who also worshipped my god. I had then realized that there were other denominations of my faith under the same god, that in time I grew to accept but still not agree with as long as they did not interfere with my goals and the lives of the innocent. He is a man, not a saint and no longer sees life and death in black and white but in endless existential nihilistic greys.

Mathais, Psalmaturge of the Gilded Spade:

|'m playing as a Grave Cleric right now as well, and we just encountered a lich in the Princes of the Apocalypse module.  Now my cleric would be ready to try to destroy this lich, yet as a Cleric of Sehanine, the Elven diety of night and death, she allows Baelnorns which are basically liches for a good purpose.  To make matters even more interesting, my elf is also a Dhampir, with a lenghty backstory as to why he was allowed to live.  This lich we encounted wasn't made a lich on his own, he was a traveling hero who was killed in battle before his time, and his righteous brother used a potion to keep him alive and it turned him into the lich, yet all he seeks is knowlege and doesnt want to destroy life, or anything else a typical lich needs.  My cleric prayed to his goddess for guidance, and she said to her, this lich was nearly the equivalent of a baelnorn, and to leave him in peace since he was aiding us in stopping the Cult of Earth.

Every single PC in D&D ever should have an undeniable reason to be in that specific group they are in. Something that they cannot ignore. Otherwise you are making a PC better suited for a solo game. It's Strahd. Surely there is so much that is terrible about him that even the most devout undead killer would suspend, at least temporarily, their convictions to deal with him as swiftly and as surely as possible. I would say the cleric could just hand each PC one 'IOU one murder' note and then play nice the rest of the campaign.

In my opinion you should strive to have a negative view towards the undead, you can then pull a marvellous betrayal possibly turning some party members against them to turn the repentant to your side and become good. This may make the player feel hurt and if it does it should stop immediately, but I recommend that you talk about this in session zero.

I personally would not play a grave cleric in that group.  There's too many people who stand against the tenets that my character believes in.  I'd probably say "this isn't the right campaign for this concept" and pick something else.