That's a great question and since I brought up T-Mobile in the first place I went ahead and dug around a little via Google. It looks like no, they do not charge the providers so I guess this was a bad example on my part. They started the program with a few big names (Apple, Spotify, Pandora, more...) and then opened it up to others (Google Play, Rhapsody, more...). But it looks like the entry cost to providers is low/free and in this case T-Mobile is genuinely trying to add some value to the customer to compete against the giants in their space.
So IMHO opinion it's still Zero Rating but consumer friendly because it does not favor one music streaming service over another. I'm not trying to promote T-Mobile, just stating the facts as I see them. The cynical in me thinks that T-Mobile doing it without charging providers is to avoid any any competition legislation they are worried about running up against.
More here: http://www.eweek.com/networking/t-mobile-expands-free-music-...