If they do allow pets there will prob be a pet deposit. Around where I live the average is 250-500 bucks, most of which are non-refundable. It is much easier to get away with bringing a cat into a complex that allows animals and just not claiming it. That way if the see it they may just ask for the deposit money. It depends what your landlord is like, I know a few that don't give a shit if it is someone that doesn't cause them problems while others will give you a month to leave right there.

You aren't going to really be able to hide it though. The land lord can enter your appartment if they have reason, but can't go through your shit. Not to mention when something goes wrong with your place the landlord's maintenence crews will be walking through, and sometimes apt manager may stop by. It is risky and I would wait until you find a place that accepts animals.