From pictures, it looks like the AIW 8500DV uses DDR SGRAM, that's likely going to be a problem with the Mac ROM. It will need edited for the proper ram timings, and we will have to find the data sheet for the ram or extract it from the PC VBIOS.
Also, I detoked the Mac 8500 ROM and couldn't find the memory timings, so I have no clue what to edit. I was thinking ATI used a binary blob for ram timings, but it looks like we have to step though the forth to find where the ram timings are written.
This isn't a small task, I mean it can be done, but is it, in the end of the day worth it?
I mean AGP Mac's already have Firewire, and the Rage Theater chip used for video capture has no Mac drivers. I couldn't get a straight answer if Video for Linux has the drivers for the Rage Theater chip, so there maybe no code or documentation on how to program driver for it.
Old computer equipment doesn't age like wine, so a very limited supply of cards and people to use them puts thing project on the bottom tear of things to do.
Better off just buying a 9200 AGP and flashing that, then buy a capture device that has Mac drivers if you need to convert old analog TV stuff to digital.