No they can not -- AMD removed a couple of pin holes from the AM3 socket and CPUs so that the AM2 chips will not fit in an AM3 socket but the AM3 chips will fit in AM2 and AM2+ sockets.

IIRC they did this because the AM3 chips have both DDR2 and DDR3 memory controllers so can be used in both AM2+ and AM3 MOBOs but the AM2 chips do not have DDR3 memory controllers and will not work with ddr3 ram so can not be used on most AM3 MOBO's and to avoid AM2 chips from being placed in the AM3 boards by mistake they changed the pin layout so that the chips will not fit !!