I'll second that. I'm a T1, I play rugby and do weights a few times a week. I've dabbled with supplements and found that they do affect my levels. Some push it up (whey protein) some down (creatine). I dont use them any more, just the protein in my diet, which isn't much. I dont eat meat every day, but go through a lot if pulses. That got me from 11.5 to 14.5 stone.
Find a good hypertrophy routine. I do 5 sets of 10 reps supersetted with something else on the same muscle group. I'll do that for two muscle groups in the same session.
There was a Horizon programme recently that said a good diet will make more of a difference than spending loads of money on supplements.
As far as it being good for diabetes I'd say yes. It does help to keep my sugar levels regulated, but nothing beats cardio.