The same could happen in AFL if a kid decided he didnt want to play for the club he was drafted to. The Hill case set a precedent in Australian law, it has been deemed illegal. The only reason the AFL still has it is because the players recognise it & choose not to take it to court.
Partly - there are no other codes or leagues competing for AFL's players - that gives the AFL community a lot of peer pressure and influence over individual players.
So, even if a AFL player challenged the AFL draft, whether he won or lost might not matter, as depending upon how the AFL community (clubs, coaches, players, fans) reacted to his legal action, he might end up being completely ignored i.e. no club would offer a contract.
A NRL player in a similar situation could always try his career options in Super League or RU.