My tangs eat just about any algae they can find, and no it not bad for them, my tangs more like a cow with fins.....lol
You can feed them normal flake food, supplement with frozen mysis/shrimp/ etc and they love dried sea weed sheets. The sea weed is important for all tangs, its part of their staple diet naturally.
Hope this helps,
No is the answer, they may pick at it and thats about it , its not in there diet to eat that sort of algae, it doesnt give them there natural vitamins, are you sure its hair algea not BRYOPSIS, if it is they will chomp on that a little more, have a look on this site, scrol down to find the dif,
http://www.xtalworld.com/Aquarium/hitchfaq.htm
and if it hair algea try this site very interesting read