some undergrowth species I grow under my red oaks here in N. Texas are redbuds, mexican plums, vibernems, beutyberry and elderberries. Elderberry doesn't need as much water as you think, the european variety at least has done good on the forest edge to full forest shade. use mulch pits near new plantings to increase water near these new plantings. I have tried to grow ginseng drylands here for going on 8 years w/ no luck, summer to dry, oak leaves to big. I also have everbearing strawberries under my oak forest and they are slowly expanding and even give a few intense flavored strawberries.
I am working on a 6th generation shade tolerant triticale, 3 generation spaghetti squash grown in shade. These are land race varieties I am working on. Chicory grows well in the woods. All these I grow in our oak overstory, dryland and have some success and failure. Good luck on your venture