No, you can select the current device in the Sonos App to stream music from, It does not need to be a service. and it does go through the application, since the music is stored there.
http://www.sonos.com/documents/productguides/en/SetupGuide_EN.pdf
Wireless iTunes playback from iOS devices
You can select and play music and podcasts stored on any iPad, iPhone, or iPod touch that’s on the same network as your Sonos system. Playback is perfectly synchronized, in any or every room of your home. Simply choose This iPad, This iPhone, or This iPod touch from the Sonos app on your iOS device to make audio selections and then you can use any Sonos controller to control playback.
Wireless playback requires Sonos Controller App for iPhone or iPad version 3.8.3 or higher and devices running iOS software version 6.0 or later.
since Apple Music will be accessible from inside the Music App, the Sonos app should be able to play it out just like it does the music library, and currently iTunes Radio form there as well.