The trackID.gxt2 file shows that more songs were planned for Rebel Radio, but they weren't included in the final version:
Bob Dylan - Subterranean Homesick Blues Commander Cody And His Lost Planet Airmen - Hot Rod Lincoln Hank Williams III - D. Ray White Jimmy Martin - Run Pete Run Johnny Cash Johnny Paycheck - (Pardon Me) I've Got Someone To Kill Waylon Jennings Also, even more songs were found in the early build of GTA V on dev PlayStation 3:
Johnny Cash - Man In Black Jon Wayne Egyptian GG Allin