I'm guessing the only way they could have caused trouble is to yes, crawl in the Dolphin Tank. But why on earth would they give someone access to that for any event? I mean come on, you don't give visitors access to stuff like that, so why would you leave an area unguarded or whatever.
Shedd Aquarium is a beautiful place, and I'm very sad to hear that anyone would even dream of vandalizing it.
Chicago love.