Will this hitch work with my existing trailer ball and coupler?

Yes, the 2" receiver opening is the industry standard. Any standard hitch ball mount or accessory with a 2" shaft will fit directly into the receiver.

Do I need special fasteners to mount this, or does hardware come in the box?

The hitch mounts at factory points, but fastener specs aren't confirmed in the product data. Verify your vehicle's service manual for bolt size and torque specs before final assembly.

Can I use this hitch to tow a loaded trailer or just a cargo carrier?

A 2" receiver hitch is rated for light to moderate towing and cargo loads. Check your RZR's owner manual for maximum towing capacity — the hitch itself and your machine's suspension must both handle the load.