Let’s start with the concepts: A direct drive wheel is a slimmed down design with a sprocket bolted straight to the hub. A cush drive wheel has a separate drive hub that interlocks with rubber dampers between those interlocking fingers. The sprocket is bolted to the outer drive hub or “cush drive”. Those rubber dampers soak up energy that is produced when a shock load occurs from hard acceleration or braking.
Another perk of a cush drive wheel? You can buy extra cush drives and bolt extra sprockets on them for a fast and easy gearing change. You’ll be able to swap gearing as fast as you can remove and reinstall the rear wheel!
Do you absolutely need cush drive on a street/supermoto conversion? No. It serves its main purpose for 600-1200cc asphalt-ridden bikes with much more power. However, a 500cc or less dirt bike can still benefit a small margin in the long run from a little less wear and tear on the drivetrain.
If you plan to race your supermoto, lose some unsprung weight by sticking with direct drive hubs. The less rotating mass, the easier it is for your bike to accelerate. Cush drive also adds parasitic loss and when you’re dealing with relatively small displacement like a 250 or 450 dirt bike, you want utilize every ounce of power, and drop every ounce of weight possible.