After a bit of pondering...
I don't think Imu is tied to any of the aforementioned Gods. When Vegapunk said the war between JB and the Kings was ambiguous, I wondered how so. Now I think we have an idea. It seems when JB awakened and became Nika, he was doing what the apparent original one did, which seems to piss off the other Gods. So, Imu and the other Kings opposed JB to prevent the Serpent from arising once more.
But the irony is, it seems Imu did such an awful job of keeping the world balanced, that Nika was allowed to come back and make a better world.
Of course, does that mean if Nika can return, can the Serpent be allowed, as well?