I have sided with the Volkihar. I've heard some people tell me the hood is accessible as random loot, just hard to find – and other people tell me it's Dawnguard-side exclusive. I would like a definitive answer. I really need this piece of clothing. What is my poor Malifyrre supposed to protect his head with in the sunshine? There's nothing that remotely matches vampire armor.

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

#X B O X 3 6 0
#No I don't care if it's a black cowl. I want it anyways.

Sadly, I've never come across any kind of vampire hood. Maybe someone else has different luck.

Not this undead Dunmer... I've never seen it in any of the loot I've ever received since installing Dawnguard.

I'd be interested in this as well.