Yes, most if not all came with Mac OS 9 pre-installed. [EDIT] I just re-checked - up to and including the "Mirrored Drive Doors" models, all PowerMac G4 models

Yes, most if not all came with Mac OS 9 pre-installed. [EDIT] I just re-checked - up to and including the "Mirrored Drive Doors" models, all PowerMac G4 models could boot into Mac OS 9.