The soundtrack is courtesy of members of the HH Alliance, Gwop Ghettas (Salt Lake City) and The Establishment (Boise) and features indie artists The Commission, Yung Verb, Venomous Ink, 50 Cal, and more.
To get a taste of what the local faction of Gwop Ghettas has been doing with their hip-hop "Gwop Swap" showcases, read this little blog by Jordan Wallis.
The Halloween soundtrack is also available on their website. Just click on the front and back of the cover art to get both sides of the release. There, you can find more info about the organization.