My only issue here is that I'm not sure if existing labels will begrudge a new competitor on the block (and then try to kill Spotify). It doesn't seem to me like Spotify being a fellow label gives them much more that the existing labels would want, but maybe I'm just not thinking of it.
According to my memory and a little research [1], the record labels have some stock stake in Spotify. Personally I think this is Spotify's best bet: if the labels can derive stock gains from helping Spotify (plus licensing fees), they have skin in the game so they won't try to sabotage Spotify. I'm of the opinion that instead of trying to produce music (and fight the record labels), Spotify is better off getting into a complimentary position: make it easier for fans to find out about concert, purchase tickets at fair prices, and buy t-shirts. All stuff that Spotify can probably do better than the record labels, and which won't cut into label profits.
[1] http://www.swedishwire.com/jobs/680-record-labels-part-owner...
The need for them to be a record label is not for exclusivity, it is so they can operate as an equal partner. At the moment their entire business is based on negotiating deals with record labels, all Spotify can offer is revenue, so they will be squeezed and squeezed as each contract is negotiated and renegotiated.
Every artist that signs up to them will save them this cost in the long run... So I'm sure there'll be seemingly crazy deals like comedians have been striking with Netflix, which in the long run are will be very beneficial to Spotify.