Pipefish definitely (I had a banded pipe in my high flow 120gal for 5 months before it got killed by my darn tomato clown) But, not with aggresive fish like wrasses or damsels or clowns.
They actually do quite well with all the flow and stay very fat and happy as long has you have plenty of mature live rock for them to hunt on.
Seahorses NO WAY. They are WAY too delicate for an sps tank and all the hazards associated with one, including other fish, powerheads, etc...