After further tinkering, my Voodoo 5 5500 card is now confirmed working, but not as intended. The vga port is fine, but the dvi port will not drive an Apple Cinema Display, or at least, not the 23" or 20" models, either Aluminum or Acrylic (the latter via an adapter, naturally). I have no way to test the dvi output on a CRT, unfortunately, as I don't have the right converter. The closest I get to a screen from it is some garbage on the two 20" ACD units.
So it may just be that I'd need an older dvi monitor with a different stock resolution — not going there, however, as I have WAY too much junk as it is. Ho hum.
There do appear to be hacked OS9.2.2 drivers for the Radeon 9200, however, and as it is a good deal smaller than another screen....