Let me guess, one member is a certain Lady Inquisitor Aestas and her retinue (work out the translation from latin - and it's something else that's on my big "to-do" list).Originally Posted by Erriond
Blood Angels aren't vampires as such, although they do share a lot of the classic imagery, and whilst the Red Thirst is a blood craving, they just consume it.
Some death cults also drink the blood of their kills, although again, blood consumption, not really vampyrism.
RT era Vampires were psychic possessors as Kage said, maybe a Dracula-type vampire could be some kind of cultist that's dabbled in certain life-prolonging arts, or maybe a certain type of daemon can possess a host, but needs blood to provide the energy to maintain it's connection to the material plane, and taking that blood then opens the body to possession by another daemon of the same type.
Maybe there's even something some followers of Nurgle's released that causes Vampyrism.