I haven't dealt with this stuff in a loooooong time, but for well over a decade, if a CPU fit into a socket without a hammer, it would not be damaged at power-on (even if it wasn't compatible). Socket 939 and Socket 940 were essentially the same, but one was for server-grade CPUs and one was for consumer-grade CPUs. They were almost pin-compatible, but not quite -- hence the very slightly different socket.
There might have been a couple of exceptions to this, but by-and-large it was the case.
So, if that holds true today (big if, granted), your CPU should be fine.
Sorry I can't be of more assistance with this.
2Yup, you just need a BIOS update if an AM2+ doesn't work in an AM2 socket. – hanleyp – 2010-04-12T03:03:43.937