No, sir, seahorses are no more sensitive to ozone than other marine fish. But, just as you say, sir, if ozone is used correctly in the aquarium there should be no residual ozone that reaches the main tank with the fish in any case.
If you can afford it, using a control unit to adjust the ORP via carefully administered doses of ozone in a seahorse tank should be beneficial, providing it is done properly. An ORP level of between 200-350 is perfectly acceptable for a FOWLR tank; you do not want the ORP level to rise above 500 for any length of time, as indicated below.
Redox Potential or Oxidation-Reduction Potential (ORP):
Normal Range = 200-500 mV (millivolts)
Optimum Level = 350 mV (millivolts)
The redox potential relates to the degree of water purity in the aquarium, and can be thought of as a measurement of the water’s ability to cleanse itself via oxidation. It is measured in millivolts of conductivity, a unit that provides information about the reduction and oxidation characteristics of the water. (“Redox” is merely a contraction of reduction-oxidation.) Oxidation-Reduction Potentials (ORP) are closely related to the stability of the marine aquarium and can therefore be used as a barometer of water quality. Highly efficient filtration, good aquarium maintenance and management, and the use of ozone in conjunction with a protein skimmer will help to boost redox values.
The best way to administer ozone for your purposes is to use a sump-mounted protein skimmer with an ozonizer controlled by any of the quality aquarium controllers that can monitor ORP, Tom. The outflow from the skimmer should then pass through a large, deep bed of quality activated carbon before it is returned to the sump and reaches the main tank.
Best wishes with all your fishes, Tom!