First of all , I mean that the policy of osu ! of " not allow to use the name of a VOCALOID bank because it has copyrights , but if the rest of the material such as MP3 , artwork, etc" is cynical .
In what way can damage the facilitate the search for what is already illegal ? And I mean illegal MP3 downloads of authors in Japan are licensed or just the Intellectual Property.
Sure, come out with the excuse that we are out of jurisdiction or any kind of things trying to defend the indefensible.
Second , with respect to what is considered as Artist , the format is usually used VocaloP feat. Vocaloid -in-use , that is, for the person who buys the album will understand that (and of course , it depends of the artist) , however , back to the issue of the legality / ethics osu! , The common of users is presented as a not aware of these habits , so it is quite complex to understand . Hatsune Miku is clearly not an artist, but is relevant to mention that it is related to Vocaloid beyond an instrument , but rather is a multimedia phenomenon. (And please, osu! should not be an Itunes).
Finally , to help restore the "chaos " caused by this huge rule ( which by the way , I think it's stupid ) , the most logical solution is to put some space as "As made famous by" form, very popular in games like Guitar Hero.
I am a fan of Vocaloid since 2007 and am currently managing an artist 's coming to Chile ( Yuyoyuppe ) , also taking with permits to use the brand YAMAHA Vocaloid in this event. However, osu! lacks everything that can be called permission , so once and for all , do this as a rule HELP to mapper / user and not make it something more dispersed.