Watch: Supergirl Batman Reference
Does Batman exist within the Arrow-verse? Well, there have been rumors that Batman might be coming to the CW DC TV universe, and a previous episode saw Clark Kent reference Gotham.
Now in tonight's Supergirl vs Cyborg Superman episode (watch the battle here), Kara references Batman when a conversation is started regarding the Guardian being a vigilante. Kara says she isn't a big fan of vigilantes (doesn't like masks) as her cousin, Superman, worked with a vigilante who used tons of gadgets and had lots of demons. "Vigilantes are nuts," Kara says. While Supergirl doesn't name-drop Batman, it's gotta be the Dark Knight!
Regarding whether or not we'll ever see Batman on Supergirl or any of the other DC series, that seems a stretch as the producers on the series basically said no. I wouldn't rule out Batman completely, however, as DC did give permission for The CW to use Superman for a couple episodes, so we could just as easily see Bruce Wayne for an episode or two. Supernatural's Jensen Ackles happens to be fan-favorite choice to play Batman on TV.
"Supergirl" airs Mondays at 8pm ET on The CW starring Melissa Benoist.