It very much depends on the specific RV model. If it's set up to be used in subfreezing temperatures, you certainly can use it in subfreezing temperatures. If it's not set up for that, you can use everything except the plumbing system. Some setups are better and more trouble-free than others; ideally, the entire plumbing system should be enclosed within the heated envelope of the RV, which means having the dump valves etc. in a compartment that is at least nominally heated.
I've used my class C motorhome in freezing temperatures without trouble. I try to avoid driving it when the roads are salted due to the corrosive nature of salt on the chassis etc. For quick trips in cold weather, I sometimes don't bother with the water systems because winterizing immediately upon returning home is somewhat of a pain and most dump stations around me (which are none to plentiful to begin with) are closed during the winter.
Cold weather camping does require more propane and battery power (if not on shore power) than warm weather camping.