Is it just me or does he always sleep on the floor behind the bookshelf in the alchemy room of Castle Volkihar??

He's the bosmer vampire that trains speech and sells/buys general goods.

I noticed that too. I thought he was dead so reloaded an earlier save (only a few minutes of time). Then I seen him the again, this time I clicked on him and he woke up. So i am guessing its just glitch that he sleeps there.

I was looking for him at one time during the day and no where to be found. Then I saw feet hanging out behind the bookcase.. last place I would have looked.

Dawnguard adds skill trainers?

Yep, it does. Iirc 2 in castle volkihar (speech and 2-h, maybe smithing? but not sure) and 4 in fort dawnguard (smithing, marksman, heavy armour and restoration, i think they're all master lvl)

Whoa so you can level up really fast then.

I don't think it's a glitch, I just think he's very far down in the pecking order and doesn't have his own coffin. He is kinda subservient to all of the other Vampires in the castle.

True, though there are always a bunch of empty coffins.

I've even seen Dexion Evicus (moth priest thrall) walk to a coffin and go to sleep... I don't know, it was weird. After he closed the coffin and went to "sleep", I bit him in non sneak mode and he got aggro and started to attack me lol. I reloaded my save game and he went and did the exact same thing, except I went into sneak mode and he had no idea I had a snack.