Just a quick question:

Despite over 700 hours into the game, I've never touched the main quest beyond Alduins Wall (don't even know if that's far in, but given the overall shalowness of the game, I suppose it is).

I recently started a redguard character I cosider completing the main quest with, but considering what a Redguard Dragonborn would do, he'd most likely side with Alduin due to him most likely being the same entity as http://www.uesp.net/wiki/Lore:Satakal#Satakal, surviving the destruction of the world and entering their Pantheon.

I assume it's not possible, but asking doesn't hurt. (Not a big issue, but if I can't, I wont touch the main quest with that character).

Not to mention the fact that Alduin rescues you from the Empire at the beginning of the game.

But no, you cannot join up with him.

Nope, no choice to side with Alduin.