I personally would not do it after I saw a TT at my local dealer with its bumper and bike rack attached barely hanging on.
I asked the owner what happened and he said another car came up along side of him on I20 pointing to the rear of the tt. He pulled over and he was nearly dragging his bikes on the interstate. The dealer was going to reweld his bumper back on.
I use a Curt front mount hitch on my truck with a Swagman bike rack. Solid and you can see your bikes. Do what you please but call your tt manufacturer and see what they say.
Good luck.