Good Question 1sagittarius - But I have an answer.
Deer do eat on the seed pods in the winter, especailly in heavy snow. I wouldn't consider it a great food source though. As far as I've seen, they rarely browse the branches.
But the reason I want it in a hedgerow setting, is to widen the hedgerow from 15 ft wide to like 40 ft wide. The hedgerow I have in mind splits two good sized fields, and connects two bedding areas. Sumac, when it grows in clumps offers an excellent canopy overhead, that will rarely exceed 20 ft tall. Yet deer can easily travel between the trunks of the trees.
Finally, in good deer country, rarely will you find a clump of sumacs without a multitude of rubs. I think the deer really like to rub sumac because of its fragrance, sap, and size. Kind of like balsam fir.
We already have a ton of aspens, and I realize I could plant widely spaced pines or spruce with a similar result. I may end up going with a conifer, in the end, I just thought that if sumac would establish, Its a 3-4 year proposition, rather than a 8-12 year one.
Thanks for asking.