What is a musicians union?

union welders do the same thing non union welders do. union welders usally get higher pay and better benifites ex. health care vision dental perscriptions and so on

yes he is

Mostly by spending time with them, working on a song, going over notes, that sort of thing.

There is no union for veterinarians (or most other medical professionals like medical doctors, pharmacists, etc.). Their professions are specialized requiring an exceptional amount of education,...

Yes.