Thompson, I've been purposefully avoiding investigating the ethics of patronizing Spotify because I love it so much (I'm currently listening to Vol. One of the Bach Cello Suites played on baritone guitar by Slava Grigoryan mentioned below on it) but here's an article from NPR that might provide some information.Click here.
I can tell you though that I donate to and buy products from a young duo based in New England that play traditional tunes from all over. They tell me that after they put their one CD on Spotify they got a noticeable bump in interest on their website.