I have gotten all sorts of hitch hickers on rock. Mostly non reef safe crabs.
Basically your going to get live stuff or you would have purchased base rock and added the creatures you wanted. If you really want to QT it I suppose you could put the rock in a spare tank and spy on it each night for a while with a red flashlight.
I would put the rock in a tub with SW, a heater, and a powerhead for a few weeks. Check for little white stars, crabs, and other large pests as you put the rock in and take it out.