According to this article about how censorship shaped Batman the animated series, that is exactly the reason that the bad guys used tommy guns, as well as the reason why GI Joe used futuristic ray guns.As I said before, the censors are concerned with kids imitating what they see. So it's not a question of how violent the weapon is, but of how likely it is that a child might have access to the weapon.
http://www.dorkly.com/post/86084/batman-animated-series-censorship