Meechams is an official RV rental vendor of the Fort.
"Read More" under 'RV Rentals'
RV folks can bundle a golf cart with a trailer rental.
As to outside golf cart vendor rentals, yes,
Disney is protecting THEIR golf cart rental business. By making it LESS convenient to use a separate outside vendor for carts, they try to make their cart rental MORE convenient (although pricier). So you either have to ride with them, drive their truck with the flat trailer (cart on it) into the Fort, or (as I have done) meet them off-site, put their flat trailer on my hitch/truck, pull the cart into the Fort, unload cart, return trailer, return to Fort. If it is YOU the FW guest coming into the gate with the cart, that is permitted. What is NOT permitted is a non-guest bringing in a cart (essentially). But bundling a cart and trailer has been permitted.
It's the same approach they use with their Disney Minnie Van service (can come to your campsite to pick you up and drop you out) but Uber, taxis, and the ilk have to pick you up at the Outpost Check-In building (and the ride services don't DARE wander back into the loop area). Minnie Van is more expensive but thus more convenient as well.
As an official Disney vendor, you're assured of receiving a DISNEY quality experience from Meechams.
Bama Ed