Never seen it done with corals... though I have seen it done with a combo of a black plastic mesh or "egg crate" and live rock... The problem with using coral to devide a tank is the coral would have to be fairly branchy and go all the way to the top of the water column to keep the preds from getting through. That and a good number of predator fish also eat or pick at corals. IF I were to do this, I would do it with a mesh of some sort as the physical berrier, then use corals/rocks to hide it, having seahorses on one side, and larger reef safe fish on the other.