Board Thread:Arrow discussions/@comment-9346948-20150811210531/@comment-4159709-20150816094946

SeanWheeler when Wells called him a "man of steel" it could have just been an easter egg for the fans, or, because Wells is from the future, he could know about the existence of Superman before Superman reveals himself to the world. So no, for that reason and the reasons the others said, like Diggle saying "What's next? Aliens?", Superman does not exist in the Arrowverse (at least not yet).

If they want to have a crossover with Supergirl they will have to explain it in a very plausible way, like the multiverse, and not just have her appear on the other shows like Constantine.