Yes, I do believe the Rito are descended from the Zora tribe in OoT. But I think 'evolved' is the wrong term here. IIRC, the Deku Tree specifically said that the Koroks once took the form of children, which to me implied they were changed unnaturally, probably using magic. Its possible the same happened with the Rito tribe.
That could be possible. maybe the gods changed the zora into the rito because if they could swim, they would see the old hyrule under the sea while the gods wanted hyrule to be forgotten.