I have.
I bred a few different species of seahorses from 2000-2006. If you want to do this I would recommend Barbouri, Reidi. Erectus do live on the reef somewhat but do not seem to be as tolerant. Other species I have tried like Comes or Whitei just aren't good for their own reasons. Any of the dwarf species would present far to many challenges with food concentration.
Temperature is the biggest thing. Yes CB can handle higher temperatures, but that means 74F tops. 74.5 not good; it's really a black or white, not much middle. It has to do with specific strains of vibrio that are part of syngnathid digestive systems. CB or WC still have the same strains. At temperatures above 74 the protein structure changes and it becomes much more virulent. Dr Martin Belli has a lot of information on this in the book Working Notes.
The second issue is going to be nutrients. If you are wanting to do a LPS or softie tank, you are good. Make sure you have corals without the nemocysts. If you want to do an SPS tank or anemone tank that is just not going to work. Even if you can dial in the flow and get lower temperature SPS, the seahorses using the sps as hitching post will kill the SPS. Barbouri is the most adapted to living with SPS of all of the species, so the seahorse won't be harmed as much, but the SPS, ya that is not going to be happy.
The other major issue is feeding. If you mean seahorses in a reef tank full of reef fish you are going to have to train your seahorse to eat from a turkey baster and feed it 6-12 shrimp 2x a day. If you mean a reef tank as in seahorses, corals, and some seahorse friendly fish that are slow eaters you will still be able to broadcast feed.
I wrote this article up about 15 years ago on tank mates that might help you
https://www.seahorse.org/library/articles/tankmates/tankmates.shtml
For flow rates, that is mostly a myth IME. I have had seahorses in tanks with a 130x turnover. You just have to break up and alternate the flow so it works for them. Spraybars under the rocks, even used as rock supports are great for this. I used to run two in my tank that were plumbed into a closed loop. If you are keeping seahorses in a reef, or in a seahorse tank I would suggest this type of water movement setup. It just keeps everything suspended so it can get to the filters. Seahorses have very inefficient digestive systems so there poop is often larger and dense. Water movement needs to plan for this so it can be removed quickly.
HTH