I did this race last year and, despite usually running with music, I didnt use mine and dont remember seeing anyone else using theirs. The race is on open but small country roads, no pavements, so using headphones would probably be quite dangerous.
I am planning on doing the race again this year but will be leaving my ipod at home. I can't see how there would be a problem with using an ipod type device as a gps without headphones.
Btw, running without music is not as bad as you think 