Even the rollers are not perfect, as ideally you'd want to generate heat in the tire in the same manner that it's generated while on the car - from lateral & longitudinal slip. To do that on a machine requires a sliding belt element and belt testers are very large & expensive pieces of laboratory equipment. Those rollers will work the rubber, but in a different way. It's still better than an oven though.
This is why race teams will go out and run a few easy laps on new tires during test or practice sessions to break them in. As long as you have the track time available it's best to just do it on the car.