Vampires in D&D can be at least neutral - another Faerun vampire elf, Jander Sunstar, is a good example. Astarion obviously was an evil person as a mortal and 200 years of torture unsurprisingly didn't change him. Someone in this thread mentioned this already but
during the first gameplay presentation Swen Vincke said that Astarion was selling criminals to Cazador's family as slaves and source of blood. No way he was good or neutral doing this.
Considering how many non-linear small things this game offers, I bet that both redemption and staying evil will be possible for him. His background story is so specific it must be.
