I'd cure it if it was mine. Just because it's dry doesn't mean he cleaned it after removing it the first time, it could have all sorts of decaying organic matter in it. And sure you could scrub it very well, but if any of that decay is down in the rock, good luck with all that. Just stick a piece or two in a bucket with an airstone and check the levels. If it's going to spike ammonia/nitrite you should know within a week I'd imagine.