this topic has always interested me. I have several observations. This year in my neighborhood there is about 80 acres of standing corn....yet while shed hunting I have only found one dead deer...and it was most likely a roadkill. Obviously the local deer fed on grains all fall and winter. I assume that because the deer had been feeding on the corn over a long period their rumens had the correct microbiology to digest it effectively without complications. So....in an area like mine....people feeding corn to deer really shouldnt be worried about the potentially negative consequences as say if it was an area with little to no agriculture and the deer are not exposed to the grains over the long periods of time.
I would think that supplemental feeding of deer in the winter would be highly dependent on the local area and what food sources the deer have available to them during the winter.