Two rumors about Celebrities and JW's.
1) {insert name of celebrity} hates JW's at their concerts they start by asking all JW's to leave.
2 {insert name of celebrity} is a JW. They were baptized at the {insert name of convention}, they go out in service with {insert name of congregation}. As soon as they finish contract requirements they will quit {whatever they do} and pioneer full time.
There have been a few that #2 applies to, but not many and certainly not equal to the number of rumors.
Over the years I've been to many concerts (including John Denver) and I've never hears such an announcement. I think most celebreties are smart enough not to piss off their fans.