It is a complex issue because even if you don't deal with label music, there are still copyright issues. I personally would draw the line at "recorded music". If a startup does not deal with recorded music (ie streaming, downloads, mashups) they are mostly OK.
One caveat, there are also publishing rights issues around things like lyrics, tablature, etc.
Songkick does not deal with any of these issues, and I don't get the feeling that thesixtyone does either.
Also, if people get the idea that I don't understand the opportunity for independent musicians etc. please research SNOCAP, a company that I partnered with for years, ended up acquiring, and also ran. That company, despite having the star power of Sean Fanning & Ron Conway, was _VERY_ difficult. SNOCAP was promoted by MySpace, which was the #1 website at the time, as well as the #1 place for indie bands. MySpace promoted SNOCAP heavily etc.
VCs view investments as "bets", not sure things, and the vast majority of those bets fail... that's how the game is played.
(Also, for the record, SoundCloud and Echo Nest are awesome. We did a deal with EchoNest at imeem, and the SoundCloud team is worldclass.)