It looks like that is using something similar to the Problem Solvers track end to derailleur hanger adapter.

Problem Solvers Chain Tensioner W/Hanger > Components > Drivetrain, Brakes and Pedals > Derailleur Hangers | Jenson USA



Some might depend on your dropout spacing and whether you choose to cold-set the frame. If it is 120mm, you'll be quite restricted with the number of speeds you can use, even if you choose off-center rims.

It looks like it would be a pain to remove the derailleur every time the rear wheel is removed.

A few track ends have an integrated derailleur hanger, but it is rare.