I read an article a few months ago on this issue. It stated that until recently USNA and NROTC grads were given preference (First dibs). However, the Navy is getting away from that due to studies of performance ratings of academic and flying abilities compared between OCS/NROTC/USNA graduates. The bottom line discovery was that it really makes no difference if you went to FSU, NOTRE DAME, or HARVARD... when your butt hits the seat, throttles are forward, and you're pointed down the runway... do you have what it takes?
I'd love to see the reference because I'm pretty sure that's not true, and hasn't been for some time.