I have not seen any numbers but I suspect the Vets are more successful in school then the typical incoming.
At my sons last Iraq homecoming (USMC Infantry) I met some of the guys who were now attending school. They said it was going well and many of their fellow students (non Vet) were not focussed on school.
I attended a local community college while active duty (retired now) and several of the professors stated the same thing. The active duty and vets were more driven to accomplish the course work with the highest possible grade (sans grading curve) than the other students.
-Traveler