Problem with using Superman in Supergirl show

From what I understand, characters currently being used in movies cannot be used in TV shows. Since Superman is being used in the DCCU, that means legally, the show can't use Superman. So he can be "in" the show, but he can't be [B]IN[/B] the show. This was given for why Batman couldn't be used in [I]Smallville[/I]. The problem with this is, the rule is incredibly inconsistent. There were no less than four Batman shows on while the Nolan movies were being made. The Suicide Squad are regulars on [I]Arrow[/I] despite having a movie in the works. So is Deadshot. They apparently can show Superman's arms but not his face? I don't know all the legal rules around it but this is just what I've heard. So, if this is true, Superman can never truly appear in [I]Supergirl[/I].

Oh and what about FLASH? Unless it's Jay or Wally. It's the same s*it.