Can you run a 220v A/C unit off a 50 amp service?

You can if there is 2 phase electricity at the plug (A and B), BUT I think both phases must match, must have the same load on them and the same ability to supply. If it were just you powering off the breaker box then no problem, but who know how many campers are powering off only one phase of the box and not the other? You cannot control that. The first response is saying this, but without much of a warning flag waiving.
Great likelihood of damage to your AC unit. Cheaper to get the 120 version.