Can a low iron saturation be a cause of fatigue in someone with healthy red blood cell counts and related statistics? I have had some disputes between my endocrinologist and other physicians on this matter. Perhaps I need a hematologist to confirm.

Low saturation . I agree, you need the opinion of a hematologist .
Depends. How low is low? Theoretically, yes, but so many other things can factor into fatigue. Thyroid, viruses, biotoxin exposure, etc.
Generally not. Generally if your hemoglobin and hematocrit are normal, you are unlikely to be suffering from fatigue. It is possible that you may be low on iron, and it would be important to find out why. You should certainly have your stool checked for occult blood, and perhaps should have a gastrointestinal evaluation for blood loss. You should see your family doctor for this evaluation. Good luck.