Yes you can, at least I did it a few months ago. I arrived and departed ORD at Terminal 1, but I had a very long layover. I went to Terminal 5 to visit the Priority Pass lounges. At security, the agent pointed out that I was at the wrong terminal when I showed him the boarding pass for my departing flight. I mentioned that I was visiting the lounges, and he said "Oh OK" and let me proceed. I think he was just trying to be helpful. I have heard that TSA cannot restrict you from other terminals as long as you have a departing flight from the airport that day.

Now, the question is, was it worth it? I had lots of time to kill, so I think it was for me. But if I would have had less time, or would be someone impatient with long lines at shuttle buses and security, I would say no it wasn't worth it. The PP lounges in T5 at O'Hare are meh at best.