they are technically reef safe, but there are many problems with have seahorses in a reef tank. (especially sps)
first of all, seahorses hitch onto the branch corals which may damage coral tissue
secondly, the high flow required for sps might disturb the horses
thirdly, seahorses thrive in temperatures below 76. reef temps are around 80.
fourthly, seahorses are messy eaters and poop alot. this means degraded water quality which is bad for any reef tank.
dont get the pair of seahorses.