So I'm running my first campaign and am having dispute's between players. So the question at hand is that way of the long death monks do or do not support the idea of undead? I have heard it depends on whether the undead is intelligent or not and some people say it's strictly up to the DM or the players own personal choices. Just wanted some feedback and to see where it goes.

I'd say its up for DM/player's choice. Every character should have ideals from case to case basis. For example, I made a way of the long death monk who was basically the grim reaper so as a result, he didn't like undead because he was supposed to bring people through into the next life. It can vary depending on the character in question.

I dont think the subclass really has a stance on the subject. It could be on either side depending on individual.

The player could have one opinion and the monastery (or wherever they leaned from) has a different opinion. Or the player could share the opinion of their monastery but there are other monasteries out there with different opinions.

It's up to you and the players. As DxJxC said - there's no stance either way in the subclass itself.