Learning by experience is good. However, the kind of training you're suggesting is pertaining to a more advanced kind of player than complete newbies. They won't benefit much from the kind of training that goes on at, say, the wwF servers. They need to learn the basics before trying to perfect their technique. Consequently, you'd need a server with a team of dedicated admins and helping players to directly teach newbies, and to make sure other non-newbies contribute to the learning of new players, or leave - unvoluntarily if necessary. You'd also need to create an atmosphere on such a server that's friendly, and in addition, you'd need to make sure the 'lessons' are both enjoyable and educational.
The succes or failure of a server dedicated to newbies is how it's set up, really (provided there are any newbies to teach). Wraths was succesful by having, in my opinion, the best admin team that could be found in Tremulous. Similarly, I think you'd need such a team in Unvanquished if you're to make a newbie training server succesful there.