Thanks for reaching out to this question. Please note that I can't answer human health questions. Here is information on rhododendrons and mad honey: 

• Rhododendron Ponticum - an overview | ScienceDirect Topics
• Vitamin, mineral, polyphenol, amino acid profile of bee pollen from Rhododendron ponticum (source of “mad honey”): nutritional and palynological approach | Journal of Food Measurement and Characterization (springer.com)

I have not heard reports of honey bee poisoning from foraging on rhododendrons in Michigan. Honey bees will forage on many plants that are in bloom, so we can expect the overall amount of nectar from rhododendrons to only be a small portion of the total nectar in the hive. It has been estimated that it takes about 2 million flower blossoms to make a pound of honey, and while the true number may vary, the point is that nectar from rhododendrons will likely be diluted by nectars from other plants that are also stored in the hive.

Happy beekeeping!