Personaly, if it were a 'pay to enter' club or if I was getting a fee, I would refuse a tip.
If it were a free entry venue I would happily consider a tip (shared if in a session) preferably liquid.
If I were busking, then I would think that is definately a cash activity.
On a lighter note, I and some Shanty singing friends decided to do an impromptue Carol singing session in a pub, in Derby UK, during the pre-Christmas festivities. A gentleman who had imbibed well, requested that we sing the Irish Rover, we refused on aesthetic grounds. Then he placed a large container of beer on our table and, unsurprisingly, we sang the Irish Rover...
"And it's no nay never, no nay never no more..."