I doubt a Voodoo video card would work correctly.
PCI cards have been problematic in G5s, and a Voodoo AGP card does not work at AGP 8X voltage.
And even if that wasn't an issue, if it is a Voodoo 4 or 5 (instead of a Voodoo 3), the colors wouldn't be displayed correctly anyway.

For the system mentioned, a Radeon 9200/9250, 9600, 9800, or X800XT with an Apple rom would be the best choice.

Alternately an X1950Pro or X1600 AGP PC video card could be used.