My vampire has deliberately slaughtered half the small towns of Skyrim with my master Volikhar thralls and has a bounty ill never be able to pay off at 3 major cities yet. How does that work?
Edit: Ok this is my theory, Volikhar is a whole different thing to Dawnguard, Dawnguard could careless if you are a vampire or not they are more worried about the Volikhar.
So the question is, will the Dawnguard quest line recognize your character as a vampire or not, sadly I can almost guarantee that it will not. They are going the mainstream route, and the mainstream of people don't like being a vampire because they don't know what there doing. "Oh geeze! Vampire Lord! Oh Im going Vampire with DLC comes out!". So the DLC quest line is likely revolved around that fact, that the DLC will be the first interest anyone has at being a vampire.
So that's fine, gotta appeal to everyone, but it would be nice to at least have a comment thrown into the quest line somewhere stating "hey we know what you are but your not the threat of the Volikhar & can still help us"
To further this, if Lord Harkon says "Or is it to become one of us, to feed on the blood of the living etc etc" I am going to light the entire Castle up in flames, Thrall Lord Harkon with my vampire and brake the entire quest line out of anger. Then reload