I think I read somewhere that it's possible to summon Dremora Lords through a ritual, kill them, and then use them as Dead Thralls.

Is this possible? The wiki article states that some enemies like Dremora Valkynaz are too powerful to use as thralls. Do the summoned Dremora Lords scale to the point that they become impossible to use as such? Or are Dremora Lords too powerful to begin with?

You get a permanent one with its own spell. It's not a zombie.

Havent found the Thrall spell yet as my Conjuration isnt up to match yet,but ive got one lvl lower,the summon dread zombie i think.
Allows me to ressurect the lower ranking Daedra.Valkynz and whatertheirnamez.

more specific example:
i can ressurect the 2 daedra inside Dagon's shrine,but not the 2 outside.They are above my paygrade.

So i reckon the highest lvl ressurect spell could work on them.

Only in theory of course AFAIK.

I'm pretty sure you don't. I did the quest for the Thralls last night and the trainer does not have a spell for a dremora thrall, only atronachs and zombies.
I really hope I'm wrong though!

Because it's not a Thrall. Unbound Dremora

I haven't been able to get it to work outside the quest. Should it? It's so low cost compared to the thrall spells it seemed unlikely to me so I only tried it a couple of times.

Doing some checking, you might be right. If you are right, that makes me sad.

You can just summon it whenever you want (magicka cost isn't too bad with the perk) anyway so its not a big deal. Honestly I find using my permanent summon slot on other dead enemies is more usefull as I can raise a Master Necromancer or other powerful NPC as well as being able to summon my Dremora Lord in front of me whenever he is needed.

i prefer summoning dremora lords when i need them. pressure plates and npc's dont go together.

It's generally better to resummon your Dremora to be infront of you anyway. Permanent summons always get stuck behind you in dungeons which negates a lot of their usefulness.

You can find some Dremora in front of Mehrunes Dagon's shrine if you really to reanimate them. Know however that Dead Thrall won't work on them only Dread Zombie. Dead Thrall only works on humans, mers, khajiit, and argonians.

Ahhh...that makes me sad. I was working on a character build that put 4 points in twin souls just to use Conjuration gear and have dremora pets.

Unfortunate truth. While having perma Dremora would be cool its not really practical for dungeon running.
Personally when I am running a dungeon I keep summoning dremora infront of me anyway
Though when I'm just walking I prefer to keep storm thralls summoned because they snipe anything coming at me.