Would something like warlocks devil's sight work on this? It doesn't state it's specifically magical or otherwise (Although, if it wasn't magic I am unsure what else it could be). It says "as long as the doors are open" and not "or until dispelled". The darkness isn't described as the darkness spell either as it was in the previous adventure White Plume. 

"The room is affected by a darkness spell, which the vampire is not hindered by because he has truesight. If the vampire needs to leave this area to pursue intruders, the door to the room is littered with tiny holes through which he can pass in mist form. If the magical darkness is dispelled, it renews again automatically at dawn." -White Plume

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If examined with a detect magic spell, the area displays an aura of necromancy.

Stunning Shadow Trap. If the doors are opened, roll initiative. Darkness immediately fills the corridor out to 20 feet from the doors. Any non-undead creature that starts its turn in the area must succeed on a DC 15 Charisma saving throw or take 7 (2d6) necrotic damage and become paralyzed until the start of its next turn. The darkness remains as long as the doors are open. -Dead In Thay

All spells are magical, but if the effect doesn't say, then it's up to the DM to interpret.

The effect of any spell is magical. Likewise, any damage dealt by a spell is considered magical (when factoring resistances/immunities). (For advice on if something is magical see Sage Advice here: https://www.dndbeyond.com/sources/sac/sage-advice-compendium#SA224 )

The Darkness from a Darkness spell is magical because it's from the spell. The spell also specifically describes it as magical darkness. The darkness from this spell specifies it blocks darkvision.

If you have Devil's Sight you can see through it.

Yes the room from White Plume is like the Darkness spell. The trap from Dead in Thay does not make that distinction 

Quote from Im_Aquaman >>

Yes the room from White Plume is like the Darkness spell. The trap from Dead in Thay does not make that distinction 

The info I provided should give you all you need to answer your questions about these. 

White Plume = magical, because it states it is from the Darkness spell.

Dead in Thay = not magical, because it is not described as magical nor is it from a spell. 

Dead in Thay probably intends for the darkness to be magical (and prevent light from entering the area), but it doesn't really matter for devil's sight, since that works in both magical and nonmagical darkness.

Thanks all!

I think where my brain got tied up was that either way, magical or nonmagical, it's still just darkness and as written it wouldn't affect those who can see in the dark. It's just dark, not blinding. (Well, because it's not magical darkness by the definition linked above)

Note, Darkvision still works in magical darkness. It's the spell that specifically states the darkness of the spell blocks it.

Devil's Sight is quite specifically a way around the spell (as this is the most common form of magical darkness).

But anyway, Dead in Thay isn't magical darkness, so its a moot point either way.

I'd argue against that personally based on the wording of certain abilities 

Devil’s Sight

 You can see normally in darkness, both magical and nonmagical, to a distance of 120 feet.

Astral Sight. You can see normally in darkness, both magical and nonmagical, to a distance of 120 feet.

Devil's Sight. Magical darkness doesn't impede the devil's darkvision.

Raw and rai I'm sure come into play here, but it seems to me if the darkness is magical you'd need special vision to see through it. (I understand the darkness spell is worded in such a way and other magical darkness probably does not come up as often. Just my personal feelings on it) 

But looking deeper I suppose that's actually true. Like Hallow:

Darkness. Darkness fills the area. Normal light, as well as magical light created by spells of a lower level than the slot you used to cast this spell, can't illuminate the area.

Unlike Darkness, Maddening Darkness, Dark Star, etc, Hallow does not specify creatures with darkvision cannot see, even though it is magical. 

Interesting! I learned something new. Thanks Cyber

This is also clarified in Sage Advice:

Does all magical darkness block darkvision?

Magical darkness blocks darkvision only if the rules text for a particular instance of darkness says it does. For example, the darkness spell specifies that it produces a magical darkness that obstructs darkvision. That obstruction is a feature of the spell, not of magical darkness in general.