I have no opinion for this thread, but taking it a step further: Do coaches have the right to tell sprinters, field events, whoever, that they must wear sweats/warm-ups on a cold day during their warm-up and cool down? Extend your opinion to this situation.
As a high school coach I require athletes to wear school related t-shirts for warm-up and cool-down. They do not have to be the same or school issued but cannot be some random shirt. This may be the issue more than showing skin or some other unknown.
No matter the team rule or thoughts concerning the situation in this thread, expectations should be clearly defined, shared with parents, and open for discussion long before a meet situation.