You can put the rock right back in. The glue gel will harden underwater.
I put a piece of shrimp for my hermits to pick at and A LOT of bristle worms came out the rock and started eating it. I thought it was awesome, I know most people don't want them in their DT but I don't mind, I like them. =]
No way to tell without a closer shot. Could be any number of LPS.