Almost certainly. Unless Bethesda took a lot of care to leave to original vampire scripts completely intact and only changed values that relate to vampires outside those scripts, which I doubt. I love Bethesda for making modding so easy, but they do tend to fail pretty hard at actually taking into consideration what people are likely to do with mods and coding around it (most notably- They never, EVER, put in a catchall else clause whenever they have anything that relates to race. Which is pretty basic programming knowledge as far as I'm concerned :/)
Also, any vampire mod that doesn't use the original vampire scripts will still be fine. Like, not proper vampire overhauls most likely, but a mod I'm working on is going to add some abilities for vampires that are an aside from the main script, so it will work just fine after dawnguard comes out.
Also, as long as the maker of the vampire mod you use is still active, it probably won't take much to update the mods to work with Dawnguard.
