I have always wondered about this. Are conjured Dremora Lords affected by the atronach part of the conjuration tree or the necromancy part? Or, since they are summoned from Oblivion are they something totally and completely different?

I ask because I dont know if my conjured Dremora Lords get the 50% more effectiveness from the Atronach side or the tree, or if they get the 100 points more health from the necromancy side of the tree.

Does anyone know this? Also, is it safe to assume that the summons from the Soul Cairn are affected by the necromancy side of the tree (the 100 more points of health)?

Atronachs are daedra as well, same as the Dremora so it probably uses those perks.

http://www.uesp.net/wiki/Skyrim:Dremora_Lord#Dremora_Lord

"...while the Dremora Lord is technically not an Atronach, it is affected by the Summoner and Atromancy Conjuration perks, although it is not affected by Elemental Potency. The Twin Souls perk also applies to Dremora Lords, making it possible to have both a Dremora Lord and an atronach or thrall."

Necromancy perks apply to "reanimated undead" so they shouldn't work for Dremora Lords as they're not zombies.

It is my understanding that necromancy perks also works on summoned undead such as the boneman, mistman, and wrathman.

Dremora Lords are affected by the atronach side of the tree. In simple terms, that side of the tree makes the Dremora Lord very powerful.