Actually, I'm quite sure compilations are included. That's why a lot of bands release a GH album just to be freed from their recording contract.
I think Jarmo is correct. I know Oasis was signed to a six album deal. So far they have released 5 studio albums and 2 compilations (b-sides, live album). Their deal runs out this summer, when their sixth studio album is released. So obviously the compilations had no bearing on their deal.
Actually, now that I think of it, I think greatest hits albums are included in a deal but other compilations are not which would be the reason why Oasis' compilations did not count.