No, an experiment should not be set up to prove a hypothesis, it should be set up to test a hypothesis. In one the hypothesis is falsifiable, and in the other it's not.
No, because people did behave differently than he expected, and he coached them to behave in line with his expectations. He wasn't a neutral observer, he was a guiding force and the superintendent of the pretend prison. This is what I mean when I say it wasn't an experiment.