Can't see any reasons against using one of these services.
1. Their contentID system makes you have to prove you are not a thief.
2. Shifting revenue stream distribution are only ever good for Youtube first and publishers second. They are a big organization now. Some would say a monopoly. If they can't get 10% revenue growth from their users they'll carve it from under their publishers.
I think YT and Vimeo are really good but even I enjoy having a healthy market where all types of players exist.
Yes, the videos could be easily found in Youtube or Vimeo, but that's not a good choice if he is building a potential revenue stream.
What he could do is just upload to Youtube some free chapters (for easy discovery), and then have some premium and charge for them. Like RailCasts.