Wait, hate to be pedantic but how could Superman have believed in Rao since the beginning if he was raised on Earth? Logically he'd share the Kents' religion, if they had one, and would presumably convert to the Kryptonian religion later when he found out about it...

...Which raises some odd questions, as the lack of other believers in Rao would surely render the worship of said deity purely an academic practice as there's no one around to instruct Clark in HOW said worship could be done.