I'm looking at the 700c Mavic Open pro rim for my cross bike, a replacement as the Velocity Aeroheads finally gave it up.

The Mavic site publishes tire pressure ratings but only up to 28 mm. I want to run 32mm clincher tires. Will this be OK?

The Mavic site publishes tire pressure ratings but only up to 28 mm. I want to run 32mm clincher tires. Will this be OK?

Yes.

I assume you are planning on running cross tires? If so, you want to keep the pressure as low as you can and not pinch flat.