Can't speak for MK but I work 3rd shifts at Epcot and the parks are well let. We have over 500 people in the park working on any given night, and that's only Disney Employees. Every building, prop, attraction, show, shop and restaurant are cleaned each night as well as all pavement in power washed. No place goes unseen.
There are also tons of contractors in the park each night that paint, clean carpets, work on pavement, sewage, plimbing, etc. Security also walk the park all night constantly checking every door, corner and dark spots (often with dogs) so I can almost certainly say...no, you can't hide.
And anyone trying should know that if they are found, be warned that Disney will prosecute to the fullest of the law. They don't mess around with stuff like that.