For Texas? I don't know how far south Dolgo fruits. I plant apples in Ontario, Ohio, and Norway. Ohio has normal midwestern weather, so options are plentiful, but Ontario and Norway have extreme weather. Ontario gets brutally cold, so I have found that pushing northern limits of apples is not a good idea. Norway is extremely rainy, so disease resistance is the most important thing to me here. I am now much more inclined to try to breed my own deer apples for extreme weather rather than try to push midwestern genes into extreme environments. I just planted out 50 seeds from apples that grow and produce well in Ontario, and when the ground thaws, I will dig up my seedling bed from a few years ago and cull the losers. The ones that are growing well will be planted out in a hunting terrain.
For Texas, I would buy warm weather apples and graft any good local apples/crabs I found. Then gather a bunch of apples next Fall and grow them out and see what you get.