One more note after re-reading the OP.
If you decide to use a vapor barrier, use CBU and then go to town.
If you decide to use CBU straight, then do CBU with Kerdi (my 1st choice)
Don't do both - Vapor Barrier, CBU, Kerdi.
You don't want to create a ~sandiwich~
I have never spoken to Schulter myself. I have spent as much time as needed digesting info from tile pros and tile pros generally prefer CBU over other bases. They will even go far to say the latter stuff like the hardie board, etc they strongly recommend to not use in Wet Applications and go with CBU if you can.
And yes, I do think a SUCCESSFUL Sheetrock/Kerdi can be done, I just think the variable where there penetrations, CBU would probably work much better in mitigating the water permeation issue...