If pulmonary function test shows a mild obstructive ventilatory defect with normal volumes and high dlco but not a smoker and don't have asthma, is this finding significant?

Need more info. You don't mention why you had pfts in the first place. The combination of a mild obstructive defect with normal volumes and high diffusion is typical of asthma. Without clinical data i can't be more specific. People with allergic rhinitis may have sub-clinical asthma. Which form of Hydrocortisone are you taking? Tablets? Topical?
DLCO repeat. The increase in the DLCO with a mild obstructive defect may still be related to asthma. Other causes of increased DLCO include obesity, exercise, bleeding or high hematocrit.
Low pulm func. It may be significant , and you should see your doctor about follow up testing. Be sure you are inhaling clean and pure air.