My refrigerators spec for level says the maximums are: 3 degrees front to back and 6 degrees side to side. Font to back is the side the door is on, with the coil on the opposite side.
Considering side to side trailer level only then:
With the refrigerator mounted to the side wall. 3 degrees is equal to .6 inches per foot.
So for a 8 foot wide trailer, the numbers are .6 inches per foot times 8 feet or 4.8 inches.
I think that most of us would be fairly uncomfortable with the rig this far out of level. That's equivalent to three 2x8s under the tires on one side. Anything less is supposed to be acceptable according to the manufacturer.
Myself I like it pretty level, so that doors do not open on their own when unlatched and eggs stay put in the pan. I also gave up sleeping uphill and down hill when we moved from a tent to a camper.
So in the end, I think most of us could probably agree that making our camper perfectly level has more to do with our comfort than the refrigerator absolutely requiring it.