I wouldn't consider a VW Vanagon from the 80's a hippie bus. Although, these day it might be the only option for some hippies looking for a Volkswagen van.
Can also be used to discribe the crazy, psychedelic painted school buses used to transport large amounts of hippie. Buses from the 40's through the 60's were typically used in the 70's. The Further Bus for example. However, hippie bus is most used for discribing VWs.
VW Buses forever, Peace everybody!!!