Honestly, I don't think music is important at all on a demo reel. I would question the validity of any recruiter that wanted to hire an animator based on their song choice.
I have actually never put music over my demo reel. Some people love putting a big rock song or a dance beat over their animation to help the entertainment factor, which I totally understand. Personally, I don't like putting anything on my reel that distracts from the animation. That includes both the music and the packaging.
I'm not hoping someone watches my demo and is entertained in the way they would be by a movie. I also don't want them spending time staring at the ornate box I sent it in. The goal is to have them focus on the work they are watching. I've heard that a lot of recruiters will turn off the volume if there is a distracting song playing, which won't help your dialogue shots too much.
I was told by a friend who has been in the industry for a long time that there was a general assumption among recruiters about demo reels: the fancier the packaging and presentation, the less likely the animation is good.
Less is definitely more when it comes to demo reels.