Personally, I believe in consensus. The events of Oblivion prove Akatosh's existence, and the upcoming events in Skyrim prove Alduin's. I don't believe they're anywhere near the same. For one, Alduin predates Akatosh--Alessia created the idea of Akatosh as a fusion of the mer god Auri-El and the Nordic Alduin. I also tend to think Alduin identifies more with Satakal, anyway. I think that the belief of Nirn's mortals causes the gods to form. I don't believe the gods need their continued belief to remain in existence.
Edit: Please select no more than three answers.