Just call me and I will explain. The license is nothing compared to what the boat may have to do or be.
1. Define applicability based upon body of water. State exclusive or navigale as defined by 33CFR
2. If navigable and they intend to carry not more than 6 passengers the boat must be operated under 46 CFR Subchapter C as a uninspected passenger vessel if less than 100 GT. (Which a pontoon boat would be). If greater than 100 GT you can carry up to 12 passengers for hire.
In both cases above the operator would only be required a OUPV license regardless of route or proximiety to shore.
3. To carry more than six passengers less than 100 GT. The boat must comply with 46 CFR Subchapter T for up to 150 passengers or Subchaper K for greater than 150 Passengers but less than 100 GT. Complying with T and or K to optain a certificate of inspection is a very heavy lift unless you really understand boats, and the rules. Not just that you may think you know a lot about boats you have to really know. I have witnessed countless individuals throw incredibly large amounts of money away becasue they had a dream and had been boating for 50 years.
If the boat is on state exclusive waters they can do whatever they want. At least as of two years ago when I checked state law. Please note this differs state to state. In Michigan you would have to mirror federal law and the state would provide oversight.