..You do know this is the same series where Kaido can become an Azure Dragon, right?
And Sengoku, a Buddha. Marco, a Phoenix. So on and so forth.
I really doubt Kizaru would be surprised about Saturn turning into an Ushi-oni.
The clearance thing is likely just so nobody tries to blab about the secret of the Gorosei. I doubt any of them besides MAYBE Akainu know who Imu is though. That kind of defeats the whole purpose of, yknow, him being the super secret leader.