While I agree with Annie you can also expect the answer is generally yes. As well smoking, poor diet (and uncontrolled diabetes) and a lack of exercise will definitely combine with the diabetes and lead to early erectile disfunction. Tell him he won't have to worry about a low sperm count when he can't even get it up for the job. Ask him how he would like that inevitable outcome if he continues with an uncontrolled lifestyle.
Not enough to count on for contraception.