Do diabetics exhale acetone even when glucose is well controlled, perhaps not enough to smell, but e?

No more than normal. Acetone comes from the metabolism of excessive ketones. When glucose levels are maintained at appropriate values, the body of a person with diabetes does not produce more ketones than someone without diabetes, and so will not produce more acetone either.
Not likely. We are all capable of exhaling acetone in tiny amounts especially when doing diets like the atkins. So if a diabetic is starving himself of carbohydrates, acetone and other esters will build up in the blood and the body will excrete them in urine and through respiration.