Board Thread:News and Announcements/@comment-9346948-20160203192559/@comment-160289-20160207224125

The main issue I see here, is that some of you only consider the plot and not the shows from a production viewpoint - what the producers mean to be part of a same universe or not.

Yes, because they exist within the same multiverse.
 * Can characters from an Arrowverse Earth travel to Supergirl Earth?

No, unless the producers specifically confirm it on an article or on the shows.
 * Does that mean that the universes where they go, are part of the Arrowverse?

One could argue that the wiki could well be about the whole multiverse, but (as of now) the producers have intended to keep them separate, and there is no problem at all in not covering the whole multiverse, just look at the table. Considering all articles that we have about the subject, we are not going to get as many in-universe connections with Supergirl as we do between the Arrowverse shows unless things change heavily in the future.