Well, I'm roleplaying a "good" character, and I'm a little fuzzy on what is and isn't considered a non-evil use of Source Vampirism. I've heard that vamping ghosts is a fast path to evil (for reasons which remain unclear to me even after the end of Act 3), and I've decided that using it to re-steal back a Source point stolen from you is okay. I guess corpses are okay too since it's either that or souls to
I would say "spoiler" alert about the Arhu thing, but fortunately after interrogating the last prisoner in the Magister's basement and talking with a few people, like Kemm's kids, I pretty much guessed that was the case already.