Stop posting Dawnguard stuff you are spoiling it for people.
Volkihar are as the guy above me said, part of the vanilla game. Though they are at present only one of the higher tiers of vampires.
Like the bloodied vampire and such.
Volkihar Vampire and Volkihar Vampire Master are the two highest tiers of Vampires in Vanilla Skyrim.
No connection to the DLC, just very powerful normal vamps.