This looks like Cushing's disease. The skin does look healthy and not itchy so it sounds as if he is comfortable for now. It's not really treatable in hamsters.
You do get hamsters who have no fur and they just require some extra care in lots of soft bedding, no rough toys to damage the skin and keeping warm. They tend to eat extra food as well so keep him well topped up. I would handle as normal if he is willing and try and think of him as just the same hammy with a coat off
There are some articles in the forum on Cushings disease.