From what I remember only some GF2 cards were Dual View, meaning they had two independent RAMDAC's, and thus could drive two independent displays.
Also, the Boot ROM update for the Power Mac G4 had an FCode ROM for the Geforce 2 MX 400( Device ID 10de,0110 ) NV10.
But a lot of PC cards didn't have as high of clock rates, so unflashed PC cards would show artifacts from too high a GPU/VRAM clock.
NV11 cards can be made to work, just need to edit the device id, and all the clocks and timings.
I don't know if NV11 is supported by OS 9 drivers, never tested it.