Of course he's there to sell keyboard - Why else would Yamaha send him to sunny Florida? That's why they hired him. Good musicians are a dime a dozen, but good demonstrators are tough to find. Additionally, Florida, especially the west coast and central Florida, is where the older folks live, and they're the ones that have the money to buy keyboards for home use. Let's be realistic here. Yamaha knows it's market and that is what it is targeting in this part of the world. They sure as Hell would not target pro musicians, which is less then 1/100th of a percent of their overall sales.
A good demonstrator, such as Bartman is worth his weight in gold to any arranger keyboard manufacturer. When he demos those keyboards they come alive. And, he can sing quite well, which is a big plus. Top this off with his ability to communicate with any audience, his charisma and humor and you have the makings of a great sales person. So yes, that's why he's there. He surely didn't come to south Florida to improve his tan.