Here's what I would do in your shoes....
I'd go the manager (not just the receptionist or assistant behind the front desk, but make an appt with whoever is in charge of the whole complex) and tell him/her that you were unaware that "small animals" kept in escape-proof enclosures were considered the same as "cats and dogs" as stated in the lease you signed. If, indeed, a pet deposit is required...and those keeping hamsters and parakeets and goldfish also pay the same deposit...then you are fully willing to cooperate.
Then I'd say, "Now that that issue is settled, I have something much more serious to discuss with you." And, being as reasonable as possible, without letting your anger get in the way of good business sense...explain that you have definitive proof that the maintenance man is snooping into people's private property. You wish both compensation for the violation of your rights, (something reasonable...say...$300) as well as his/her assurance that this person will be dealt with accordingly so the matter never happens again. Do NOT make threats at this time about going public or bringing in lawyers or anything like that. Don't put them on the defensive or back them into a corner. Give them a chance to make it right first. IF they balk and refuse or blow you off....then bring out the promises of unpleasant publicity and/or lawyers.
Good luck with it!!