I'm using an iPac with my G3/300 B&W.
The GGG gamepad encoder would probably work, but I'd worry that you may run into software limitations on the number of buttons supported.
If you're really into vector games, I'd look into using v.30-v.33 for the vector games.
The vector emulation back in those versions was alot better than the newer versions for some reason.
The other notable jumps in quality/speed are around v.60, and around v.77.
Just prior to v.58 (IIRC), and somewhere after v.60a there were controller problems, and speed issues, for the older comps.
Somewhere around v.77 they switched to OSX only, IIRC.