In one of my previous careers I was a nursery manager. I can guarantee you that there are probably a wide variety of apple trees that would do well in Oklahoma. I'm in south central Texas and if they do well here with our extreme summers, lack of rainfall and lack of cold winters they should do really well there. Fruit trees, (not including citrus) grow and produce best in areas with a decent, measurable amount of rainfall and chilling hours in the winter months. You've got us beat by a mile on those things.
Never Trust A Skinny Cook!!!