Jess,
Just did an index finger for a guy who experiences tendon problems in his ring finger, so he uses his index and middle finger now. I was very skeptical of it, but he ended up liking it, and bowled fairly well with it. The thing I found unusual about this particular style, was the ball doesn't really sit in the palm of your hand, it is more off to the side. He still seems to get decent revolutions, since he is still using only 2 fingers, but I still find it unusual. I recommended that sarge easter, but he was more willing to try something that is rarely done, lol.
Had he added an index to the existing grip, and used 3 fingers, I could see it working fairly well, but this was just goofy, but hey, he likes it so i cant complain.