I don't know if any of the chemicals used then damage the pancreas (diabetes), but it's a somewhat fragile organ and if you have a genetic weakness in it (as I do), it does not take much to cause havoc. I am fortunate in that my lifestyle was and is such that I have not had much impact from it and once off the prednisone that stress tested my pancreas, I did not need insulin. I have been told by people who know more about such things than I do that 95+% of the people who had the issues I did would have died. I PT pretty hard and have for years, which seems to have carried me through.
Military and chemicals: Agent Orange is far from the only problem from that time period. Camp Lejeune has a pretty bad history with various chemicals and health impacts, see
Camp Lejeune: Past Water Contamination - Public Health. My FIL served at a Nike facility in the Guard after active duty, and there were more than a few of his fellow soldiers who died of various cancers (rare stuff - for example, his was one of a single digit number of cases known in the world) probably related to all the crud with which they worked. The collective ignorance of the rest of the Country with regard to Hazmats applied at least as much to the military, and the regs for protective gear were slower to come to the military.
In essence, we shall probably never know how many of the men (and women) who served from the late 40s to 80s were lab rats without knowing it, and without their commanders knowing it. There may be some culpable behavior, but I doubt we can ever be reasonably certain of that.