I'm not at all convinced* Apple (or Motorola, PCC, et al) ever produced a driver for PS/2 (for MacOS). Those were there for PREP/CHRP compliance on the clones. Apple, even on their LPX-40 (Tanzania) 4400/7220 didn't have the PS/2 populated, unlike Motorola's StarMax line which was the same board, essentially. Just one gesture on how Apple felt about PREP/CHRP, I suppose.
My own (anecdotal) experience on my StarMax (no drivers at all, just plugged in pre-power-on) is that PS/2 mice work rather terribly: horrible click latency to the point where you have to do geriatric clicks (read: hold down longer) to get it to register. And since 3rd party Mac mice were ADB, it's doubtful right button support is enabled at all on a device plugged into the PS/2 port. When I plug in a standard PS/2 mouse the right click just freezes the mouse until you let go… I would also have infrequent cursor position latency, but that wasn't precisely repeatable.
I don't recall my experience testing my Dell PS/2 keyboard, but I'm sure it was similar to the mouse experience. I can test that again, too.
TL;DR MacOS didn't have specific PS/2 driver support AFAIK and have seen in clone maker installation disks, *though I haven't had an image of PowerComputing's MacOS 8 disc to test…
Did Umax ever have a MacOS 8 disc? I know they were still making 603/604 systems which *ahem* might have shipped with a G3 card in a separate box…