I don't remember any CP/M system with the BIOS part in ROM (and BDOS loaded from disk). It would be possible, of course, but every subsequent version of CP/M for that machine would need to be able to work with the "frozen" BIOS, and I'm not sure CP/M was designed thinking of mixing BIOS/BDOS versions.

Saying that, I think the Epson PX-4 and PX-8 had CP/M in ROM.

Having said that, Alan Kay has seen things we people wouldn't believe, so, if he says it happened, I'm betting on him.