Diabetes and MJ...

Well as nicotine according to studies raises blood sugar, if you are smoking MJ with tobacco there will be a detrimental affect on blood sugar levels.
As to any other linkage I don't know.

I don't know about impact on blood sugars (honestly I've seen all sorts of claims in both directions but not investigated whether there is good evidence behind any); however you might consider vaping or edibles to avoid the smoke-related ill health effects.

Smoking and diabetes are both risk factors for coronary heart disease, strokes and high blood pressure to name a few. So
smoking as a diabetic will double your already high risk for these.
It's worth doing some research on google to find out the exact risks... there are loads of journal articles out there.

As far as MJ is concerned, have you thought about making tea? I have never been a smoker, but in my early 20's may have been known to dabble in the occasional bit of weed (I had severe insomnia, it helped). I used to make a tea by putting the buds in an tea infuser and putting some fruit tea in with it to make it more palatable.

Vaping will not help the active ingredient that affects blood sugar is the Nicotine that has been shown by a recent study.

though you can buy an E liquid that contains MJ extracts. Or so I've been told.