I was toying around with my PowerMate USB on the Mac.
I noticed that in the PowerMate application, you can set triggers for mouse wheel scrolling. But some applications coughMAMEcough don't pick it up.
Investigating I found that it provides its spinner as a uncommon HID type. So applications ignore it, not knowing how to handle that.
The click is presented as a normal button though. So no big deal there.
brew install libusb
brew install hidapi