No PowerMac G4 with G4 built-in by Apple has built-in SCSI access. (a few people have some upgrade CPUs whose firmware may still support 9 booting,
inside the PowerMac G3 beige).
PowerMac G3 beige was the newest G3 with built-in SCSI access. It supports up to Mac OS 9.2.2 and Mac OS X 10.2.8.
PowerMac G4 MDD 1.25 Ghz with no Firewire 800, but with built-in Firewire 400 supports Mac OS 9.2.2 booting, and can take either Firewire SCSI from now defunct OrangeMicro and Ratoc, PCI SCSI from ATO that support in some cases up to Mac OS X 10.4.11, or USB SCSI adapters. Its maximum OS is Mac OS X 10.5.8, though under 10.5 and above, can't use Classic, but can still boot 9.2.2. It does require a 9.2 installer disc that came prebundled with it to install 9.2.
Powerbook G4 pre-2003 1 Ghz models with rear mounted USB and Firewire ports are very similar to the PowerMac G4 MDD 1.25 Ghz in their support, except you'd be looking at PCMCIA cards to try to accomplish what the PCI cards could do.
Powerbook G3 Bronze a.k.a. Lombard are the last with built-in 29 and 30 pin (for SCSI Disk Mode you need the 30 pin adapter) SCSI. These could boot up to 10.3.9 if their CPU wasn't misdesigned (a few were), and they came also with built-in USB, unlike the PowerMac G3 Beige.