Well, the new government would probably ally with the US at first, but the populace will likely have great respect for Tehran. Largely, it depends on what East Arabia's political situation is like-what ideology its leaders follow, and whether they remain popular with their citizens or not.
I think in the case of Wahabis taking over the west, East Arabia will, by contrast, end up a secular, authoritarian republic propped up by the US. Something like Turkey at the time; for super-extra bonus points, make it a member of NATO!