It rained while I was there a few weeks ago, and they seemed unbothered by it. The rocks grip nicely, and if anything, it'll wash the dust and mud off the steeper obstacles. Expect it to be cold.
I believe we were at the same event. It was really a great day, plenty of rocks to crawl over, I think if there was more water in the creek we would have had a nice crossing as well. The roadrunner track at the end was an added bonus for sure; I could have spent the day there. My guide was...