Apartment companies (the ones i have dealt with so far), don’t seem to care unless someone specifically complains about you. And a lot of them don’t care if the animal is in a cage or tank. At my last 2bed/2bath apartment we had:
1 dog(deposit paid)
2 cats ( 1 cat deposit paid since the other showed up halfway through lease)
5 snakes (kingsnakes, boas)
11 lizards (geckos, bearded dragons)
5 salamanders (a communal viquarium)
1 rat
8 frogs (a communal viquarium)
Granted not all of these guys are in individual cages. Quite a few are breeding groups, so they are housed together 2-6 to a cage. But still, if the apartment management knew, they’d probably flip their s*#!. But since we are quiet people and so are the pets, no one asks questions. Even our neighbors don’t have a clue.
Personally I wouldn’t even mention the ferrets. Just keep them clean and caged when maintenance people are supposed to come around.