I've ridden on gravel before on my PCX, no issues whatsoever. You can see from this image of me riding on the beach that the ground clearance is reasonable, at least 6":
(The bike almost fell over right after the above picture, stand + sand = fall down
I don't recommend riding on sand, but I had no issues at all riding on the beach. I've ridden on some gnarly gravel and bottomed out on a couple of potholes, but the centerstand took the impact like a champ and she kept on chugging.