I made time and added one new Red 7 artist to Musicbrainz. The process is pretty easy. Because it was a new artist and release nothing appeared to be held for review except the cover art.
However, despite a Plex Dance and the use of Musicbrainz tags for Album Artist and Release Group, Plex is still combining the two Red 7 artists from MusicBrainz into one Plex artist.
Maybe there’s a delay in propagating new data from Musicbrainz to some Plex cached copy, I don’t know.