>>1
The film was produced in part by Disney, but animated by Toei Animation in Japan.
I think--people--I guess I mean otaku, are freaking out a little much. The character in question is slender, big-eyed, and has long twintail-like appendages, so her silhouette is undeniably (sometimes) reminiscent of Hatsune Miku, sure. But she's also a freaking robot, with no facial features or clothes. The long ponytail-like-things that are the source of almost 100% of the resemblance actually transform into different shapes during the show, so for much of the time she doesn't look anything like Miku.
Disney/Toei are just trying to create something that will appeal to a fanboy audience by drawing on anime archetypes. It's not as if the Hatsune Miku character's all that original-looking, either--she bears a strong resemblance to dozens if not hundreds of other popular characters. Put Vanilla H from Galaxy Angel into ponytails, for example.
Also, I think the obsessive Hatsune Miku cult is a prime example of the fundamental social sickness that plagues Japanese culture. People would rather be obsessed with fake girls--really, really fake, in this case, since she's a program designed specifically to imitate human singing--than talk to real ones.