Yes, if a person with diabetes has used all his stores of glycogen, both endogenous or exogenous glucagon will not be able to increase the serum blood sugar due to the unavailability of glycogen stores in the liver to break down into glucose. Assuming that this person has developed hypoglycemia secondary to mismatch of insulin and carbohydrates due to overdosing of insulin, decrease in carbs consumed or post-exercise induced hypoglycemia,  I believe there will be circulating levels of insulin. However, neuroglycopenia results from a low circulating level of serum glucose that is unable to get into the brain. My understanding is that you do NOT need insulin to get glucose into the brain. So, IV dextrose is required to increase circulating levels of blood glucose that will eventually make it to the brain. Thus, I don't worry too much about circulating insulin levels in this situation.