According to everymac.com, the specification site I use, there were three imac G4 800Mhz's and two of them could boot int OS 9.0 whilst the third could not -

iMac G4/800 (Flat Panel) 800 MHz PowerPC 7445 (G4)

Order No: M8535LL/A*

Model No: M6498 (EMC 1873)

Model ID: PowerMac4,2

This model is capable of booting in MacOS 9 and using MacOS 9 applications within the MacOS X "Classic" environment.

iMac G4/800 17-Inch (Flat Panel) 800 MHz PowerPC 7445 (G4)

Order No: M8812LL/A

Model No: M6498 (EMC 1936)

Model ID: PowerMac4,5

This model is capable of booting in MacOS 9 and using MacOS 9 applications within the MacOS X "Classic" environment.

iMac G4/800 - X Only (Flat Panel) 800 MHz PowerPC 7445 (G4)

Order No: M9105LL/A,

Model No: M6498 (EMC N/A)

Model ID: PowerMac4,2

This model is capable of using MacOS 9 applications within the MacOS X "Classic" environment. It cannot boot into MacOS 9.