I got wet on FEA last summer. It was annoying because I wasn't expecting it. I was in the front row. I had my camera out; I was worried about it. I would have appreciated a thread like this so that I was prepared. So, OP, thanks for posting about your experience.
I'm having a hard time understanding how a poncho could possibly be a safety hazard. When it's rainy season, people wear ponchos all day long. They are making every one undress and hold their wet ponchos before getting on the ride? That seems really weird to me.