Sea hares are probably the best hair algae eater out there, plus your fish won't bother it.
Having said that, species to species they all eat different things. Plus each animal is different. I've heard that hares won't eat chaeto and love nori. My hare munches on my chaeto and won't touch nori.
It's really a craps shoot specimen to specimen. But if you find one that likes hair algae, it will be gone in a week because these things eat whatever they like constantly.
See if you LFS will get you one and take a chance. Just be mindful of your power heads so they don't make mince meat out of it. Just know that when the algae it likes is gone you will either have to try different stuff until you find something it will eat, or find someone else who has the same problem and pass him on, otherwise he will starve to death.
As said before though. The algae is just a symptom of a problem with excess nutrients. You need to address that before worrying about the HA.