The juggalos seem to me to be a next generation deadheads. I wouldn't seriously call either a cult, but it does demonstrate the human propensity or instinct or whatever it is to want to belong to a tribe. It gives people a sense of worth, belonging, identity and purpose. I had an employee who would go to various goth/rock events and my wife's nephews go to some kind of medieval gatherings.
The term cult varies in context. In the context we are talking about I would look at it as a construct when a person or persons, the cult leaders, manipulate people's natural tendencies to want to belong to a tribe for their own personal gain. I don't know much about the Insane Clown Posse but it seems that they are just in the music business and like to party. Same as the Grateful Dead I guess, though I could never stand their music.