It depends on many factors, but it is doable with caution. First, I'd say do it in as large of a tank as you can. The only clowns that I would consider are ocellaris. Try and get them to bond with a seahorse safe host - One pair I have loves hairy mushrooms and another hangs out in xenia. From my experience, those that have a host stay in a very small area. Actually mind don't even seem to notice seahorses as being fish, and only once did I ever notice them bothering seahorses; when a seahorse was actually hitched across the hairy mushroom pair's eggs.
Wrasses you'll be pretty limited with, but six lines do well most of the time. Most fairy wrasses will do fine too. I like the purple headed fairy wrasse (also called ruby or red headed, depending), they're very peaceful fish.
Gobies, you'll have a hard time finding one that WON'T work.
Blennies you have to be careful with. Most of the algae eating ones will harass seahorses to death. However swimming blennies do fine (for the most part). I would still keep an eye on them.
If this is your first tank; then I suggest building up the animals slowly. Always a good policy, but especially in this case because it will give you time to familiarize yourself with the interactions of the animals and what is normal behavior. If this is your first time to saltwater, I would start with gobies, after six months, get seahorses, after a few more months, get your wrasse. After a few more months, get your blennies, and last, the clownfish.
You will have to watch with feeding too, as mixing these types of fish can easily out compete seahorses for their dinner. I would recommend training the seahorses to a feeding station.