I didn't know much of Frankie and the Four Seasons before Jersey Boys, ABBA before Mamma Mia or Queen before Priscilla Queen of the Desert but now I have seen them I enjoy hearing the original bands so much more!!

So I think no, you don't have to be before (but it does makes the music more enjoyable if you know the songs, but I prefer to listen to OBC recordings pre show), but you definitely will be a fan after!!