Okay, so the 'hate on sight' thing with Vampires is annoying, to me at least. I personally don't intend to incorporate that aspect of gameplay into my ongoing story, so I've experimented with ways to negate it.
It seems as if vampires and werewolves who are already family members (brothers or sisters, for example), don't lose established friendship (just don't ask your vampire sibling for werewolf sympathy, because it will annoy them and give them a tense buff). For other sims, unless they were already previously friends with a vampire, they will get varying levels of red bar dislike as soon as a vampire is near them, but you do seem to be able to get around that by either a) performing a bunch of positive social interactions until you get the vampire to like you, or b) using MCCC to cheat the relationship levels.
Honestly this is a minor annoyance for me and has not taken away from how much fun I'm having with this new pack.