Marijuana does nothing to affect blood glucose levels either direction. Glucose levels in type 2 diabetes are maintained by weight loss, exercise and reduction of carbs. The only effect marijuana might have is to give you the munchies when you might eat things that could raise your blood sugar. If you are having trouble maintaining blood sugar in target range talk with your doctor about putting you on some meds.
Not being a medical professional, I wouldn't take my answer as gold, but I can honestly say that it is highly doubtful. Marijuana rarely helps maintain anything. The only reason it is allowed in California for cancer patients is to ease their sense of desolation, from what I understand.