I loved them in my fresh tank, fun to watch and goo at what they do. They also would spawn fairly frequently
CuC in a seahorse tank.. Havent kept a seahorse tank..yet, but from what I have read snails are the best for that. Many crabs and shrimps can add a bit of competition for food and with seahorses that can be a bad thing since they are such slow movers. Others who have kept seahorse could weigh in on that one and provide a bit more insight.
There are quite a few posts up on the forum though of others who kept or were thinking of keeping seahorses.