I don't see why not.
I occasionally ride on top of, but not clipped into, my pedals - usually the mtb (Shimano) pedals, but occasionally on my road Speedplays, too. On the road, I usually do that as I"m approaching an intersection and I'm not sure if I'll get the light or not. I'll unclip early, and ease up to the intersection, resting my foot on the pedals (and doing a few revolutions of the cranks, too). On the trail, I'll do that if I'm at a sketchy section where I think I'll want to dab (put a foot down).
It's not the most efficient use of your pedalling, but it's not impossible, either.