There are no problems running System 8 on a UMAX clone, they're clone license allowed them to install 8.0 all throughout '97 and half way into '98.
I have System 8.6 running on my C500 out of choise (I don't want to spend gobs of money upgrading the expensive EDO memory) and it runs perfectly. In fact, of the machines I use daily, this is the most stable (it gets heavy use). I've had OS 9 running on this computer (to test it out and to make a CD image) but I didn't use any of it's new features and it just took up more memory, so I went back to 8.6.