It doesn't matter which format it's recorded in, but for the record, VOs generally work as .mp3 files when put into the game. For whatever reason, the files are encoded as mp3s, but saved with a .wav extension. You don't need to make the extension .wav to get new VOs to work.
Actually, come to think of it, other than Kaevee, we could use some efforts to voice a Lt. Yima, Nebelish/Dustil, possibly Dessicus.... I'm sure there are a few others too.