Not really.
There are many species found in the wild at higher temperatures, however the situation is different in our closed systems.
Most seahorses are carriers for certain strains of vibrio that multiply rapidly and are far more virtulent at higher temperatures. At these higher temperatures 75F+ they actually release and manufactor different proteins which are far more virtulent thent he proteins they release at lower temperatures. In fact at 68F they stop reproducing completely.
In the ocean where dillution plays a major role a seahorse can live in these higher temperatures without concern because of dillution, however in our closed systems the bacteria's quickly reproduce and there population increases very quickly.
Most often times there will be an initial stressor which will leave the seahorse more suseptable to infection, then you have a case of vibriosis.
IME there is not a species of seahorse I would keep over the temperature of 74F. I have found other things (such as corals) more tolerant of lower temperatures, but IME seahorses really need the lower temperatures to thrive long term.
For more information about seahorses, temperatures, and disease care there is an excellent book titled Working Notes, that is currently available.
HTH
