If User Soundsources are used in Patches or Multis being published, they will be included as part of the exported package. User Soundsources are created by importing your own audio into Omnisphere and they are automatically stored here:

Spectrasonics/STEAM/Omnisphere/Soundsources/User

Omnisphere will not publish Factory Soundsources or Soundsources that are in a different location than the User folder specified above.