Umm, not quite. GSP manhandled Koscheck in wrestling a fight or two ago. Koscheck is the guy who pretty much trains Fitch's wrestling.
In jiu jitsu, GSP is training with Renzo Gracie and is now a brown belt. The Gracie's don't give away belts like some trainers do, and a brown belt is very good with Renzo.
Fitch is no slouch either and has his black from Dave Camarillo but the way he teaches is it incorporates judo and is different. Also much easier to get a black in, although not a cake walk by any means.
GSP should have the wrestling and submission edge.