Depends what you mean by WELL. Any singer, folk or not, needs to be able to put a song across and hold the audience. If you can't hold your audience then it doesn't matter how good a singer you think you are.

It's when they stop and listen that you know you've got 'em.

I don't have the best voice, I have pretty poor timing and even worse guitar technique. BUT, when I sing a song, I make sure that they listen and remember.