I myself have the same problem that I seat profusely all the time and it's really embarrassing. At night I sweat really really bad too. My wife gets upset because she says that it has some weird odor. Back to the sweating all the time, I go through 3 to 4 shirts everyday from sweating. It's hard because I have told my primary doctor and my neurologist about it and no one can give me any answers about it.
I have noticed over the past two weeks since joining the gym that my skin on the left side of my chest, lower back and stomach is sore to the touch even my shirt rubbing my shin is uncomfortable. There is no redness or bruseing, my skin just hurts kind of like a sun burn but no sign of burn. What could this be?
When a person gets hypoglycemic, they often sweat profusely, and if the sugar drops extremely low, there is sometimes a sort of coppery smell to the sweat. I don't know if this is the same as what you are describing, but it may not hurt to have a glucose tolerance test done rather than just a fasting glucose test so he can find out if his sugar drops too low when he eats. This could be happening if he eats large evening meals and then reacts by overproducing insulin.
Honestly I don't know-but what I do know is that if you suspect diabetes you should make sure he goes to the doctor and gets some bloodwork done. Some symptoms of diabetes are frequent urination, feeling lethargic, mood changes, weight loss, feeling very thirsty and nothing quenching the thirst. Often their is a sort of fruity smelling breath. Maybe he has some sort of hormonal issues going on because of the sweating. Maybe having his thyroid tested too would be a good idea.