I did this from a G4 to a G5 PowerMac and it worked fine... but I did an upgrade to the transferred system (from 10.2.8 to 10.3.0) before I even tried booting from it.
I would expect that those two systems are close enough in hardware that the OS from one will run the other, but were I in the same situation I'd go ahead and do an "Archive and Install" on the cloned system before actually trying to boot from it. Just safer that way, and you'll be sure you're not mucking anything up by having the "wrong" components in there.