Actually, I really am lost as to exactly what the relationship between ATC and CS really is. I think CS might own ATC, but ATC only supplies CS with certain hawks. IOW, I think CS owns ATC, who produces the hawks for both of them, but they sell different lines. Oddly enough, ATC won't even link to CS off their link page.
IIRC, CS and ATC are independent entities. The conflict comes from the fact that CS registered ATC as a trademark, but never did anything with it. When the real ATC came into existence, producing Vietnam style military hawks, CS was in a position to hassle them legally for trademark infringement. So there have been legal ructions between the two companies.