I have an Apple smart cover on my rMini. I have the WiFi+LTE model. The aluminum part of the back is completely flawless, but the plastic window for the cellular radio (that isn't on the WiFi model) is very scratched up. If you have the WiFi-only model I wouldn't worry about it too much.
I will also say that I think the smart cover absolutely sucks. As a stand, the three-fold thing is useless and not at all stable. I'd look for a third-party smart cover or case before buying the Apple one.