I'll take a stab at it. Anyone feel free to correct me.
The amount of rock has more to do with how many fish and inverts you can keep. They produce ammonia which your rock converts into less toxic nitrite and least toxic nitrate. I do not believe that corals produce ammonia, so there's no direct correlation between corals and your biological filter.
A new trend, actually, is to use very little rock in stony coral dominant tanks and to allow the growing corals to "become" the aquascape. Spacing and lighting issues aside, I don't believe the amount of rock will be a limiting factor, provided it's adequate for your fish. Ammonia kills everything.