I don't see a problem with it. There is a better chance of not getting hurt when you are relaxed. Being aware of an impending collision with result in your tensing up.

Seriously I don't think that riding with headphones=death.
It depends on the ride, your headphones and the volume. I listen to podcasts on my comute and can still hear my surroundings.

Personally I think riding with a full bladder is much more distracting than headphones. Wonder if there are any studies relating accidents to the urge to piss. Maybe to be safe, Depends should substitute for bike shorts.