Seeing as I am a radio DJ, I think I can offer some useful insight here:
1. The idea that DJ's cannot pick the music they play is VERY true. Outside of college radio, the only DJ's that pick their own music are dance mix DJ's like DJ Tiesto(he has a syndicated mix show in the U.S.) and Pete Tong(he's internationally syndicated). And even they make out a playlist beforehand.
2. Most DJ's don't really care for 70% of what they play.They can't let their musical tastes get in the way of getting the best jobs they can find.
3. As for looking up obscure/semi-obscure acts, i suggest The Secret History of Rock by Roni Sarig and Unknown Legends of Rock by Richie Unterberger. The last one comes with a CD of some of the artists mentioned in the book. That's how I found out about Nick Drake, ESG, and The 13th Floor Elevators, along with a lot more!