this idea is extremely RETARDED pure and simple
the reason for consuming dex shakes post workout is derived from guys who slam insulin at the higher levels. so of course, people started parroting that info as gospel and then supp companies got in on the action pushing this strategy.
a normal gym rat does not need to consume sugar post workout. we get TOO MUCH sugar in our american diets as it is.. adding more is just plain STUPID
how about going home and preparing a healthy nutritious meal instead? that would yield superior health first and foremost than these stupid dex shakes, and the people pushing this nonsense (along with drinking chocolate milk post workout, another retarded idea) simply do not understand nutrition and failed a community college nutrition class or didn't pay attention
and to answer your specific question on if it will cause a rise in insulin and increase chances of diabetes.. the answer is it will make you more insulin resistant yes, which will increase the chances of you developing type 2 diabetes down the line.. i wouldn't go as far as saying that it will cause it. but i can tell you it will increase many more issues. remember sugar is a magnet to disease.
the less sugar you get the better is my point