It could be just about anything. This could be diet related, health/medically related problem, cleanliness related to his living conditions from his previous owner or overgrooming from lonliness and depression. I don't know if gliders can get mange (spelling?) or not but it looks as bad as that.
This baby really needs a Vet check A.S.A.P.
Whatever it is it looks awful. Once you get the Vet check done then your options should be narrowed down based on what the Vet says. I rescued a glider in pretty bad shape and his diet was awful and he was alone. Now he is doing great but the first thing I did other than change his diet was take him to the Vet for a wellness check and fecal float and smear and have him Neutered.
I assume you have already changed his diet and you have cleaned his cage and pouches or anything else related to him that you received from his previous owner. Chances are it's diet related and lonliness/depression over-grooming but really get him to a Vet to rule out any major problems as we all know that they are very good at hiding their physical illnesses until it is to late usually.
Watch for self mutilation and if need be you may have to put him in an e-collar if he starts doing that. here is a link:
http://www.sugarglider.com/glidergossip/topic.asp?TOPIC_ID=22429
and:
http://www.sugarglider.com/gliderpedia/index.asp?Collar
Do you have a Vet? Let us know if we can try to help find you one.