Hatsune Miku is not an artist. In fact, the guidelines of using vocaloid commercially (how most of the songs are distributed) state that you can't use the names of the characters in the song metadata itself. None of the doujin artists that produce the bulk of vocaloid tracks use the vocaloid's name as the artist, because it is incorrect. The fact it is being used this way on osu! is wrong.
"feat." is the best proposed solution thusfar. Personally I'd leave the vocaloid names in tags (possibly without a space so they can be grouped for searching).
"feat." is the best proposed solution thusfar. Personally I'd leave the vocaloid names in tags (possibly without a space so they can be grouped for searching).