I had lost a couple of sunburst seahorses to a "lawnmower" blenny also. Even though these blennies are considered "reef-safe", my blenny would try to scrape the algae off the seahorses just like he scraped algae off of the rocks. Ended up killing the seahorses via infection through the blenny bites.
Skygunca, I think you are right. The more that people share their learning experiences the more often other seahorse keepers will find a happy solution for their ill or injured pets 🙂