It was definitely Ray Charles, trust me. The reason I didn't respond was because I was out, I don't sit infront of my computer for hours on end. It really was Ray Charles singing, trust me. As someone mentioned above, same with the Judy Garland movie. Why not use the brilliant original? It makes it more realistic and in my opinion, BETTER. That's why RAY was nominated for best sound mixing, I think, and it will probably win for that reason.
"If you are going to do something, do it well. And leave something witchy."
-Charlie Manson