The problem here isn’t that “Van Morrison and the Chieftains” is just an alias for “Van Morrison” at MusicBrainz (it actually isn’t on the alias list).
The problem is that Plex does not support crediting an album or a track to more than one artist. A long-standing feature request, if implemented, would fix this.
MusicBrainz actually credits “Irish Heartbeat” to “Van Morrison” and “The Chieftains” (two separate artists, not an alias for one).
