Can a youtube video be created so when it is done playing it is hyperlinked to a website? Could it be programmed to automatically take them to a site at the video ending or would Youtube technology prevent that?
that is TOTALLY against the entire scope of Youtube and a video site like it. the best you can do is offer the viewer a reason why they should go to your site, and then end your video with a link they can type in. You can also put a link in the description that they can click on if they want to. Some people use the annotations to put links in - avoid this, if you put too many annotations people will NOT go to your site, they will simply stop watching the video.
Your right, best way is just to add your own link to the video at the bottom with a watermark have it blend it on enter and then fade out in the end.
but Youtube does provide API to disable link back to Youtube. Usually when you click on the videos, it links to that video in Youtube. You can disable that.