Yup.
Well, technically (*puts on blue tie*), Vocaloid is a software and vocaloids are personality avatars for that software. There are or have been about 45 vocaloids in and around three generations of program. Vocaloid 2 is when the craze, centered around the personality avatar Hatsune Miku, a 16-year-old girl with permanent headphones and blue hair, went huge. Since then there's been a handful of other really famous avatars (and the associated variations in program sound) too. Composers, both amateur and professional, seem to buy into the avatars, often keeping somewhat true to the character in the works they create. And of these composers, indeed there are thousands considered stars.
They are, as the saying goes, big in Japan.