The PowerCenter Pro's CPU card should work fine in the Apple; however, the Apple CPU probably won't work in the PowerCenter Pro (if you still have it, that is).
The PCP was based on the Catalyst motherboard design and requires the DRTRY (data retry) line from the CPU, which means Power Computing and the upgrade card manufacturers had to add it to the card pinout. I'm guessing Apple just left the line disconnected, so you shouldn't have any problems. Don't kick my ass if the machine blows up, though.