Technically, the camper can be surprisingly angled and still have the refrig work. What I have read is that over time, sometimes a long time, a small amount of out-of-level on a regular basis can slowly cause issues with the refrig.
Many, many threads and years ago, someone here suggested leveling your camper until your Stove is level - makes cooking so much easier. If your stove is level but your refrig is out of level, your camper has much more serious issues than leveling!