Yeah I read the title and thought it was a sail squirrel - you know, the ones that are road killed and run over repeatedly till flat.
I never saw or heard of mange in squirrels. I know it is common in foxes, coyotes, and wolves. We stayed in some hotels in Africa where i worried about it - it is called Scabies when it infests people. Several of my co-workers used to take their own linen over there when they traveled.
I guess if you could live trap him you could spray or dip him (I bet spraying is easier and safer unless you can dip the whole trap) and he would likely grow more hair.