AMK: The airboat pictured is legal on this particular point because although he is sitting high, there isn't decking from under the seat to the gunwales. As I clarified in my second post above, its not the seats, its sitting or standing on a high deck without a railing (while on plane). Similarly, in CedarRiverScooter's build, his seats are on floor-mounted posts not a high deck that extends to the gunwales/transom and not on the engine cover equivalent of a deck. One example that wouldn't be legal (in MN) under this point is the fully-decked flats style boats called texas scooters, which are designed to directly step on and off a lot for wade fishing, etc.
I am going to bow out of the legalities now, rather just enjoy the cool builds.