Rozalin - Voice
I have no bloody idea who voiced Rozalin in the English version of Disgaea 2; Nippon-Ichi Software America is terrible at crediting their English-speaking voice actors. If I were to guess, it'd probably be Wendee Lee. However, it's rather hard to distinguish, since I thought Rozalin's voice actress did an excellent job at portraying Rozalin.
Her Japanese seiyuu is Tamura Yukari. I'd hate to say this, but this is a game where I feel that the English voice acting is superior to the Japanese voice acting. When I tried to play through the game in Japanese, I simply could not hear the "acting" in the voices. It sounded bland to me, but the English voices brought it to life.
A few notable roles that Miss Tamura has performed are Eclair from Ouran, Kyoko in Boogiepop Phantom, A.I. in Fullmetal Panic!, Nanoha in Magical Girl Lyrical Nanoha, Tenten in Naruto, and Ichigo in Onegai Teacher.
There are a few dialouges changes I've noticed, though. I'm not a student of Japanese, but I can hear a few things. In Japanese, Rozalin uses a derogatory form of addressing people, "kisama". This adds another air of superiority to her character, I think.