Well, an LC PDS Ethernet card was about the same price, came with a driver disk, and openly claims compatibility (so I can complain if it doesn't work,) so I went with that. Since there seems to be only one LC PDS video card that's even accelerated (the Envisio Quick16,) and I can't find one listed for sale, it shouldn't be an issue.

Speaking of video, is there a way to force MacOS 8.1 to allow me to switch to higher resolutions? This model is listed as being able to do up to 832x624 in 8-bit color, but the Monitors control panel won't let me select anything above 640x480...