You're going a bit beyond my understand here but from what few studies we have, it's my understanding that we absorb nicotine with the e-cig through the mucosa in our mouths rather than our lungs like cigarettes. I'm not really sure if that would be a viable delivery system for diabetics, especially since we are only absorbing a fraction of the amount we intake. I'm not a scientist nor a medical professional though, so you can take that for what it's worth.
As to the tobacco companies, according to someone from the boards who knew someone, (you know how that goes) at least one tobacco company was working on their own design of e-cigarette. Whether that worked out for them, or they're waiting for the FDA to make a determination as to tobacco product or drug delivery device before they market, I have no idea.