Yes, often there will be one or several leaders within the group or squad who are responsible for creating the tracks that are performed to. The technical proficiency with which these mixes are created varies greatly.
Typically cheerleading squads do not mix their own music but instead hire a local DJ to mix the music for them. Run a quick search online to find a DJ in your neighborhood that would be willing to mix music for little money, if not for free.
Cheerleading squads most often have custom mixes made for them, to ensure that their music is original and not used by anybody else in the competition. There are several places online that can do this, as well as local businesses.
Unique music is really vital in cheerleading, so custom cheer music is kind of a must have. It's easy enough to get some though, with sites like cheersounds and local businesses (as Micha said)
There are places out there that mixes the music for them. www(dot)cheermusicmixer(dot)com is an example of a place that mixes the music for cheerleaders. There are DJ's that will do it for you, either for some money of free. It just depends on the Cheer group.
