Complex sentence: These original Uruks were of Sauron's breeding, but Saruman bred his own, these are shown to have resistance to sunlight and an upright stature, though whether or not these features are unique to his Uruks is open to question.
Split into simpler sentences: These original Uruks were of Sauron's breeding, but Saruman bred his own. Saruman's are shown to have resistance to sunlight and an upright stature, though whether or not these features are unique to his Uruks is open to question.