Warmer temperatures *can* work for seahorses; that's the temperatures we find them living at in the wild. However, aquarists over the years have had a lot of trouble with bacteria, and the single easiest way to help prevent those issues has been to keep seahorses at lower temperatures. Seahorses seem particularly prone to bacterial infections in aquariums.
The reason for that is not well understood, but it is thought to be because they don't have gut-associated lymphoid tissue. It's missing because seahorses lack a true stomach. Gut-associated lymphoid tissue is found in most vertebrates but is curiously missing in seahorses. The implication is that they don't encounter a lot of pathogens in the wild, but they do in a crowded, organic rich aquarium. Thus, an easy place for bacteria to proliferate, especially at warmer temperatures.
Cooler temperatures are a safe guard against that. There may be times and places to experiment with warmer temperatures, but the first seahorse aquarium is not the place. I would never recommend temperatures above 74 for anyone but the most experienced seahorse keepers.
Matt, if you feel comfortable setting up your aquarium that way, then go for it. However, I would refrain from making recommendations about systems and fish you have no experience with. It's a recipe for disaster with anything; not just seahorses.
In general though, hooking a seahorse tank up to another tank is usually not a great idea - the big one being seahorses are just waste producing machines and will likely foul your reef tank in a way that is unacceptable.
Ocean Rider recommends higher temperatures because it works for *them*. A few years ago they were selling temperate seahorses as tropical because they didn't have any problems. They didn't have any problems because they had huge flow through systems connected to the ocean, which is one of the ways you can keep organics and bacteria at a minimal level. Unfortunately, the home aquarist does not and all those temperate seahorses were struck with bacterial infections such as tail rot, and most, if not all aquarists lost them. Those that didn't came later, realized the problem and got a chiller. Oh, and the sad part about that? It was Hippocampus capensis, one of the only seahorses actually considered endangered. While they weren't hurting wild populations having those perish, it is none the less incredibly disappointing.
Ocean Rider these days is primarily a tourist attraction. They do still sell some seahorses, but their focus is on the tourist side. And their reputation over the years has been less than stellar. I would weigh that when you consider their advice.
