I would say Visual Kei is a general movement or some sort of cultural phenomena in Japan, it's not only found in musicians. But you can identify a visual-kei band if they wear elaborate clothing, make-up, and such. Some say it's a musicial genre, some say it's a sub-culture. Examples of notable visual kei bands would be Luna Sea, X Japan, Malice Mizer, early Dir en Grey, Kuroyume, etc.