Let's face it--the early, great and important collectors weren't particularly "moral" by today's standards. Lomaxes (John A and Alan), Sharp, Kennedy, Grainger, Warner, Henderson....none of them, as far as I know, even considered paying informants or sources. Not to mention Record companies, like Folkways and Leader, who either negotiated contracts which were unnspeakably one sided (by today's standards) or just didn't pay recording artists at all.
      Let's also not forget that, without these people, none of us would have any access to folk music whatsoever.