Can weight training prevent diabetes?
It will definitely help reduce the chance of developing type II diabetes, but not prevent.
Even though it helps, it does not mean you should start consuming large amounts of sugars thinking you're fine; there's a limit to everything. If you are going to consume large amounts of sugar/related, make sure you expel the energy out of your body through for example an intensive workout that drains your energy level.
I should also state that there's a positive correlation between age and chance of developing diabetes. I am pretty young, and can cope with sugar well for now, but as you age, try to consume less and less. Your metabolism plays an important role in this, a faster metabolism helps cope with sugar. Working out will speed it up (metabolism), but age will slow it down.