A GoPro won't give you enough distance itself to be able to see what you are shooting at beyond 20 yards. Torry Pines makes a GoPro adapter thing called the DeadEye or EagleEye that could work, if you want to pony up $1000 for it. It records through your scope and would work really well. You may be able to get by with a Tactacam, but again good video would be dependent on your shot distances. Otherwise trying to self film at night with a video camera would be down right tough to do, especially on moving targets.
If you tinker and research, you can swap out the lenses in a GoPro if you are inclined to tearing apart a $300+ dollar camera. There may be some other options and ideas out there that other guys know about though too.