I doubt that "nomad tenant" would be understood without some kind of explanation.
Squatter? I think of them as not having a rental agreement at all. Do Mietnomaden not have Mietverträge?
Do Mietnomaden have a record of multiple evictions for nonpayment of rent (rent arrears)? Or might they switch flats before they actually get evicted? I ask because "serial evictee" might fit for AE. That term is not widespread either, but I think it would be easily understood.
In AE, reverend's "deadbeat tenant" would be instantly understood as a tenant who doesn't pay rent. It doesn't necessarily imply that the tenant makes a habit of this, but it could work well in many contexts. However, in addition to lacking the reference to a pattern of behavior, the emphasis is very different: deadbeat is very negative, whereas in my ears, Nomaden could be heard as carrying a whiff of romance/the exotic. "Serial evictee" is not as pejorative as "deadbeat tenant", but not romantic at all.