OHOHOHOHO~
Oh, and, how about an actual KH/Vocaloid crossover like so-
The Vocaloids are playing KH or something and they get sucked into the world, appearing on the other side as cosplaying versions of the KH characters.
It's a classic scenario.
Think about it.
There's a very big roster of Vocaloids to fill the huge roster of KH characters.
xD