Actually just about all of the underwater video from the above URL was from the Walker Downrigger Strike Vision system. They used GoPros for the rod shots and I believe one small other bit.
The biggest problem for towed under water camera's is camera stability. You will need to find something to stabilize your camera which will not be that easy.
From the video I'm pretty sure their lures were only about 5-10 feet off the cannon ball, if that helps you any. (10 feet for the flasher and bait and 5 feet for the spoon). I would recommend an fish shaped cannon ball or cannon ball with a rear fin to also help stabilize the camera.
Good Luck to you.