I think they do have to be pre-approved by the EOs basically as a clause that says any unsafe spinners can be refused entry if they're not safe in the arena. That very rarely happens however, the beetleweight arenas can contain anything you'd be able to reasonably fit within 1.5kg. Most if not all spinners are just approved because they're safe in the arena, but like Jamie says it definitely applies to the lower classified arenas more than the class 1 and 2s.