Reef tank temperature is usually too hot for seahorses, and if you put seahorses in there it will not be a refugium for anythin, as the seahorses will eat it.
The space in a 10 gal. will not really be enough for the seahorses, unless you get something like dwarves, and they dont like the reef environment much.
Finally, seahorses are messy, and they will affect your reef water quality.