Both. So far as I'm aware, no one has actually succeeded in getting OS 9 to fully load on an unsupported model. (I seem to recall some thread where someone seemed like they'd at least gotten a boot started after sufficient hackery on some model, it might have been an unsupported eMac or iMac, but I don't remember the details.)

One thing that is worth noting: there's a *very persistent* urban legend that even G5s can run some special version of OS 9 that's buried inside the hardware diagnostics disks, and if only somehow the system file from those disks could be hacked into an OS 9 install everything would magically work. It's been definitively debunked: even though the hardware test environment for whatever reason looks like OS 9 it's not.