Ricardo, it's been my experience that clubs that are snuffy about who plays only applies to them that they pays. The club singers are the heart and soul of their circle "leading the line" so to speak, the paid guests are there to broaden the colour of event and to mix it up a bit, lest it should ever get boring, also, to bring in fresher songs (not neccessarily new). Me, i just like singing with lots of people I am not a good listener, I have the attention span of a gnat and a memory to suit!
Peter