Why not!
What have you against greeters at Wall Mart!
They are fine friendly old folks.
But what makes you think someone needs to derive a complete income from songs anyway?
I think that is an absurd proposal and would suggest that all musicians should have day jobs and real careers. There is nothing keeping them from music is there?

I believe that most musicians could do much better than the Greeter jobs you seem to think they might be limited to.
Folk music needs to be a part of everyday life and not exist only as a career.
Conrad