All the wheels I use for races are radial laced in the front. I haven't had any problems with them.
My Bontragers with the low spoke count are my training wheels and they are even radial laced. They are 20/24 and I have never had a problem with them. In fact, the Bontragers seem very sturdy to me. I don't know whether that's due to the bladed spokes or just the fact that they seem well built.
I also try to make sure my tire pressure is well suited for the terrain. With really bumpy courses I run less pressure, so the wheels (and my body) don't seem to take quite a beating. The pressure needed would be dependent upon your weight as well.
Again, I don't have any experience with the Zondos, but I think they'd be just fine as cross wheels.