I think games are a good way to learn things, but they have to be entertaining and self-contained. Just like typing games have to be somewhat amusing and guide the typist in their quest. Even still, the person who uses a typing game must have some sort of ambition to learn how to type.
If one has to read documentation to complete your game, I don't think it will get much attention. Let's face it...if people aren't willing to read documentation or use Google and then post somewhat basic questions on this forum for their real-life problems, they probably aren't going to do so for a game.
There would also be a heck of a lot of topics to cover, so keeping the levels concise would be important or the game could go on forever. I've been using FreeBSD as a desktop for over 5 years and I learn new things every day. That said, I would steer clear of programming languages as part of a BSD intro, especially C/C++.
Good luck!