Maybe, but...
most sea hares don't have very long life spansl;
most sea hares come into the hobby near the end of their lives;
sea hares will eat all types of macro algae;
sea hares can be killed by power heads, filter intakes, overflows, nipping fish and picking inverts;
most sea hares consume a lot of food (and thus may need supplemental food in the form of nori) and produce a far amount of waste.
I'll just say it, since I'm sure someone will at some point: your best solution is getting at the root of the problem (the nutrients feeding the algae problem) and manual removal by the human reefkeeper. Sorry, but I've heard it so many times myself...