Did you try the CD for unsupported G4's?
It looks like the 1Ghz eMac with the Combo drive supports native boot of OS 9, whereas the 1Ghz eMac with the Superdrive only supports Classic Mode.
Generally speaking, the only thing Apple changed was removing 'RISC' and 'RISC2' from the 'compatible' property of the device-tree replacing it with 'RISC3', thus preventing the Superdrive eMac from seeing the Mac OS ROM as a bootable :tbxi.
Oddly Everymac lists the 1Ghz eMac as having USB 1.1 and an optional AE Wifi card. That would be the only Mac I know of with USB 1.1 and AE, and leaves me to wonder if I bought a Combo drive version with AE, would it work under OS 9?
The info on Everymac could be wrong, maybe the Superdrive eMac 1GHz really has USB 2.0?
Or you could not order the AE card with the Combo drive version?
Wouldn't it be cool if the 1 Ghz Combo drive OEM OS 9 Install CD had the 'holy grail' OS 9 drivers for AirPort Extreme.