I don’t use Volumio to browse music; I only use it as a DLNA renderer–I browse music from my NAS running MinimServer using a control point called Hi-Fi Cast on Android. So, this may not apply.
But what I have discovered from experimenting with MinimServer is that the only artist tag that cannot have multiple instances of the same tag is AlbumArtist. So, say for the album Brubeck and Bennett: The White House Sessions, you could tag each track with multiple artists (Brubeck or Bennett or both) by having multiple instances of the artist tag (track 16, for instance, could have one artist tag with the value “Dave Brubeck” and another artist tag with the value “Tony Bennett”). However, the AlbumArtist tag would have to have either “Dave Brubeck” or “Tony Bennett” or “Brubeck and Bennett” or some variation.
Having multiple instances of the artist tag lets the track show up under both Brubeck and Bennett when browsing by artist.
Vorbis and FLAC tags natively support multiple instances of one tag; for mp3, I use ID3v2.4 because this seems the most compatible with multiple instances of the same tag, but someone else might be able to correct me.
Again, none of this may apply to browsing in Volumio, but maybe this is helpful.