Two answers, the second one making the first probably-irrelevant:
1) Coons are not going to break THROUGH a decent thickness of lexan, but most cheap greenhouses of that type that I've seen are built in a rather wibbly and pry-apart-able kind of way, and raccoons could certainly do THAT. Ask yourself, what could the strongest person I know, if armed with visegrip pliers and a small prybar, do to this? Thus, I would not trust it too far. But in point of fact,
2) unless this will be in perpetual full shade in a climate that never gets close to freezing (let alone below), you are not going to be able to keep chickens in a lexan greenhouse ANYhow -- they will COOK when the sun shines on it, and you will have severe condensation/humidity/frostbite problems in wintertime unless one whole side of it (or so) is permanently open. It might, or might not, be possible to salvage the frame and *some* of the lexan to reconfigure into a usable coop or run... but unless your situation is very very unusual, it wouldn't make a good coop or run "as is".
Good luck, have fun,
Pat