there are 2 types of mange:

-sarcoptic: which is the same as scabies in humans it is very very contagious. Once treated it does not return unless the dog contacts it again from somewhere or something (foxes are natorious for sarcoptic mange)

-demodectic mange is a mite that is found on most dogs, ussually it causses no problems in most dogs. Demodectic mange is still kinda a mystery in a way. You can treat it & it may go away for some time but it is very likely to return again & again. Interceptor (a heartworm med) can help this problem but a pill is needed everyday which would cost a fortune for a large dog like that. Sometimes (fairly rare) it can become so severe & meds dont really help that it can litterally take the life out of the dog. Here are some links to some sites w/ info.

http://www.mesavet.com/library/mange.htm
http://www.barkbytes.com/medical/med0019.htm

I strongly suggest you speek to a vet before adopting this guy as it can be very costly to treat when flare ups do happen.

Also just a forwarning, a lot of dogs look very ugly with this & obviously it affects their skin which can be become scaly & whatnot, is your friend willing to come up with money for vet bills & look into the inner beuty of the dog?

Deffiently is a cute pup!