The approval to incorporate Bruce Wayne and/or Batman actually doesn’t come from The CW — it comes from DC Comics.
The first way The Flash started handing out subtle hints that Batman might be a thing in its universe was the newspaper clipping from the pilot episode.
However, there’s also a chance that the Arrow, The Flash and Supergirl writers have been strategic about these mentions and what they mean for the Arrowverse narrative.
The most obvious Batman allusion on Arrow was the inclusion of Ra’s Al Ghul and the League of Assassins as a major part of the narrative.