IME Cleaner shrimp seem to be a case by case experience. Personally I have kept a cleaner with my seahorses and been fine, but found other speciments of seahorses and cleaners completely un compatible.
If the sehaorses have been living with the cleaners for two years and you have never observed a problem they might be alright.
If you haven't tried to free the seahorses I would very gently do so. IMO I'd go with the lower temp like Anne Suggested, and use the Neomycin (neosporin) on the wound directly. I also might venture over to your health food store and drop the $8 on Beta Glucan and start to enrich the food with that to help stimulate the immune system. My biggest concern would be for a secondary infection, which is very common with injuries and high levels of stress (you have both)
HTH, JMO