I know that it will act as a generator , working With motors and generators i over 30 years but if any others ESC will let the Power og the"wrong" way I dont know.
And if any other ESC With BEC will tolerate a back up battery as I have I dont know either , but for sure I know With Jeti it Works.
I will look into Your solution but does that eliminate my RX swithc? and what about charging the backup battery , in my system the bec does that