Yes. I have a friend who has shipped an iPhone game developed on a hackintosh.
That said, I've personally found them to be problematic over time. We're a 6-person Mac-based game developer, and we picked up a Psystar hackintosh out of curiosity. We had an intern work on it for awhile, but it had some weird quirks. The biggest problem is updating must be done manually and carefully. The longer you have it the more work you're creating for yourself, if you want to keep current, which is pretty much opposite the goal of using a Mac (less work/maintenance over time).
That said, I've personally found them to be problematic over time. We're a 6-person Mac-based game developer, and we picked up a Psystar hackintosh out of curiosity. We had an intern work on it for awhile, but it had some weird quirks. The biggest problem is updating must be done manually and carefully. The longer you have it the more work you're creating for yourself, if you want to keep current, which is pretty much opposite the goal of using a Mac (less work/maintenance over time).