Not specifically. Not specifically fentanyl. But any drug capable of causing extreme sedation, which includes any narcotic in overdose, could make someone unaware of the normal sensations that tell us we need to eat. Thus, hypoglycemia could follow. Alcohol specifically is an intoxicant that can cause hypoglycemia.
Not in itself. Fentanyl patch are strong opiates. If one would be so sedated as not to consume the proper amount of nutrition, then perhaps they could develop severe hypoglycemia, especially if they were also diabetic and taking their diabetic medications at the same time. Fentanyl alone as a side effect or by its mechanism of action, cannot cause low blood sugar.