I rode there a couple of years ago and brought my clipless pedals with me and had them installed on a rental. I'm so used to riding clipped-in and was not comfortable with the idea of riding platforms after 10+ years on clipless.
I say do it.
If you're not sure about how your bike will hold up at Diablo, get a rental.
Either way, you'll have fun. Get there when they open, ride until the lift closes, and don't get hurt.
You can have them install pedals that you bring?