DON'T buy the factory hitch. Get an Exechitch; far superior, although a little more costly. Several differences here:
1] It's rated for 7,700 lbs, while the North American factory hitch is rated at 7,000lbs.
2] The standard dealer hitch requires you to cut a good sized hole in the rear lower valence. The Execuhitch requires only a tiny notch on the underside that is not really visible.
3] When your hitch ball is not mounted in the receiver, you can barely tell you've got an Execuhitch installed, all you can really see is a tiny flap on the edge of the cover for the electrical connection.
4] The Execuhitch is THE factory hitch for European BMW dealers. The only reason I could imagine they chose a different hitch for N.A. is that the Execuhitch is a little more tricky to mount the hitch into the receiver; perhaps they felt US buyers were too stupid to figure it out. Perhaps it's just they felt the US market needed a 2" standard receiver. (You can buy a 2" receiver connection for the Execuhitch, if for example you want to install a bike rack. They also sell their own bike rack. I did neither since I just put my bike(s) inside the car.)
BMW Hitches :: BMW X5 & X5M - Execuhitch - Manufacturer and Retailer of Hidden Tow Hitches for BMW, Mercedes, Subaru