OC is absolutely fine, Grapeshot. I've OC'd there several times. Sometimes, just because, I've stopped and spent a lot of time asking questions about whatever project or vendor is set up on either side of the MMM booth.
I've also been approached by other gun owners while there. Most have told me they prefer to conceal, and that's fine with me (though I wonder why they bother to tell a complete stranger they're carrying ...) I OC'd throughout the Charlie Daniels Band concert a few years ago!
All that said, I didn't realize it was this weekend. Not going to be able to attend, unfortunately.
The first time I went, I was concerned that they'd use school buses to transport attendees from the mall parking lot to the festival grounds, but they didn't.