Does your dog have Hyperglycemia: (diabetes) Higher than normal blood glucose level, or Hypoglycemia: Lower than normal blood glucose level. If he is Hypoglycemia (Low blood sugar) then you would give him the Karo syrup. If he is Hyperglycemia: (diabetes) you would administer insulin. Have you taken the dog to a veterinarian? The vomiting could be a sign of another underlining problem.
Vomiting as far as I know is not a sign of hypoglycemia. They will lack energy. Listless, In severe instances, even seizure. I would call your veterinarian. You could also research this more on
http://www.peteducation.com