I can only say what happens in the UK. We do not have the same principles re tipping entertainers. Most paid entertainers do not as a rule get or expect tips as they are paid proper rates for the job so do not need to rely on tips. It is considered tacky. Sometimes guests do buy drinks which in certain cases is acceptable. Sometimes entertainers are not supposed to drink so we have to be careful. In all cases the simple rule is to ask the organisers what rules apply and what you can and cannot do and what is acceptable. That way you do not step on toes or break rules.
Tipping jars are usually only used by street buskers.