I agree with T. Seahorses could have major issues with many species of corals commonly housed in Reef tanks.
There are some corals that can be housed with Seahorses, but it's more like a "corals housed with Seahorses" thing then "Seahorses in a Reef tank" thing.
Low-to-medium light, moderate-to-low flow, and non-stinging corals like polyps, xenia, gorgs, and small (button) 'shrooms can be OK.