There is also a nice pub up in Lochranza overlooking the sea and the castle where there was a guitar hanging from the ceiling just waiting to be played, so I would guess they encourage music there.
Years ago when I first took my wife there, there used to be a fair bit of impromptu music - I remember a gloriously drunken rainy afternoon spent in a bar in Whiting Bay playing songs on a couple of borrowed guitars which just happened to be behind the bar.
Sad the Folk festival isn't still going. Along with the organised paid for events there used to be great lunchtime/afternoon sessions in the bars around the island with some excellent performers.
Hope you have fun - one of my favourite places in the world. Usually go up each year but have missed out for the last couple.