Yes my #1 alignment gripe in the BG games was always about Viconia. The kind of "evil" that she was was something that should have allowed for her to be a part of a good-aligned party. But it is extremely difficult, not to mention a management pain in the ass, to try and keep her. The worst part is that by the end of the saga she can have evolved to being a more neutral character, but of course it is too late at that point because you never get to keep her in your party (as a good party) in the first place. So it's a classic catch-22: she needs to evolve to be part of a good party, but she needs to be in your good-aligned party in order to evolve. You can't win either way.
I've managed to keep Viconia in my good aligned party even up to Throne of Bhaal believe it or not, I just don't invite characters that will become hostile towards her, and I balance out my reputation. It's not impossible, but it is not easy either. Personally, I don't see how evil aligned main characters would tolerate having her in their group. The only kind of person who would welcome her is someone who isn't bigoted and willing to trust someone despite their race and racial background, and those personality traits usually fit a good aligned character. Besides, while romancing her, Viconia progressively learns how to trust, and I don't see how she can learn to trust someone from an evil aligned main character because evil aligned characters generally trust no one but themselves.
