The boy scouts does not specifically require a uniform but does state that if a uniform is worn it must be worn properly. for those of us on the us side of the pond that means no kilt. out Scottish brethren have no such prohibition and it is an accepted variation of the uniform per the uniform policy in Scotland. Venture posts (another branch of the scouting organization) have more freedom in their uniform and dress. An individual post is allowed to set the uniform for that post and each post is independent of another. There are a number of venture posts that have adopted the kilt as a uniform and it in that situation is completely correct.
Cheers,
Jeremy