Complete shite written by someone who hasn't a clue. Don't do this, the pup is too young both physically and mentally.
I'd wait until at least 10 months, but even more if it is slow to mature. Keep up the basic training meantime, it will pay you back massively in the long run.
No harm taking the pup along to watch once or twice (but I have never done that either), however, don't let it mouth the live rabbit and don't let it chase.