I play two different vampire clans, and while the Modern clan try to live like humans sleeping at night and feeding from plasma drinks etc, the Traditional Clan (leaded by Vlad, of course) only feed from sims. They often keep prisoners to feed from, but especially when their household gets bigger, they also feed from random sims during the night. And - they don't put up a performance wanting an audience, but they don't mind if observed, either. Being seen might build them some respect, and in my game the clan controls Hollow, where they also control the residents. Nobody would dare to report a vampire attack.
On a side note, I wish those random sims walking by an ongoing feeding would react more often. Most of them hardly care at all.
