Roar doesn't have a "legal" tire, other than if you goto a Spec Tire race. In which you will be running the same tire as everyone else.
The 27 in the take-off is their temp. recommendation for that tire. Like a cs-22, cs-27, cs-32 and so on. Same with Sorex and RP. Each company list a tire for different Track temps.
As for inserts same thing. There are no "ROAR LEGAL" insert. At most BIG races you will be required to use a pre-mounted tire. (one that the manufactuer has mounted) That makes the racingthe same for everyone.
Hope this helps.