Been wondering a bit about hunting myself. I've had similar issues with my no-labors-besides-Hunting dorf sitting in the dining hall, quiver full and crossbow in hand, for days on end, with ample prey to hunt. Also - is there any way to get hunters to put on and keep a shield or any other armor? Or does the hunter 'uniform' completely destroy that possibility? Is the only way to protect these poor saps by throwing dogs at the hostiles in front of him?
The uniform removes that possibility. If you're hesitant to using untrained hunters, you can always enlist them first and have them train up marksdwarf (note though if they don't have the skill to begin with, they can get a negative thought for having no military skills prior to being enlisted).
As a last resort if you're having issues with getting your hunters active:
1. Try enlisting all of your hunters into a squad together, make the squad active, then make it inactive. Sometimes weird prioritization happens when rangers go to pick up ammo that was designated as someone else's.
2. This one always works for me. Make a squad with all of your hunters, and make sure it's shift is only active with one squad member at a time for one month. That way your hunters are constantly re-equipping potentially squad prioritized equipment. (and vice versa)
Make sure if you use either method, set the ammo count to very low!