I had a rubberlip in with my breeding pair of Rams and within a couple of hours of them laying eggs the plec would gobble down the eggs even with the rams trying to brutalize him.
Unfortunately I agree... fish love to eat eggs, so if you are really intent on breeding, keep a "spawners only" tank IMO. Otherwise, breeding is sporadic and luck-intensive at best.
Thanks for the info everyone! Thats what i thought would happen too. I already have three other GBR breeding tanks. I might give it a try anyways. Nothing to loose.