Okay, time for the exercise physiologist to chime in on this. This is information from current research journals....
"Smoking dramatically increases the rate of absorption of the ß agonist terbutaline and decreases subcutaneous absorption of insulin, increasing dosage requirements. Smoking also acutely impairs insulin action leading to insulin resistance." Using inhaled insulin compared to subcutaneous injections increases the amount of insulin abortion in smokers. Keep in mind, the study was done on "inhaled tobacco" and most likely not cigars.
A major concern with diabetics is hypertension - nicotine is a hypertensive and could add to the cardiovascular complications. Blood pressure above 140/90 is at higher risk. A secondary complication is hyperlidemia (too much fat) - nicotine increases the amount of free fatty acids in blood stream - again leading to enhanced cardiovascular risk. Again, keep in mind that enhanced blood nicotine levels are associated with inhaled tobacco (primarily cigarettes).
The insulin sensitivity to nicotine is primarily acute, meaning that taking insulin immediately before or immediately after having nicotine may not be the best thing for you if you are insulin dependent.
Nicotine tends to effect Type II diabetics stronger than Type I - couldn't tell you why.
....and finally, there are limited to no research studies on cigar use and human health so we need to take all these studies with a grain of salt. How much we smoke, what we smoke, and how we smoke play the largest roles. Fact is it is smoking is not a health enhancing habit, but limited cigar smoking (usually determined as up to two cigars per day in most research studies) shows very limited to non-statistically measurable deficits in health. Health effects are show with a higher number of cigars smoked per day (4 or more usually).
Hope this helps some.