As usual with NRL, it's as clear as mud, but I'd be very surprised if the scheme can be used that way.
This is how it was described at the time it came in:
“If a hooker goes down we expect a hooker to be signed and if an outside back goes down it will have to be an outside back,” Gardham said.
NRL clubs are expected to be more supportive of representative football after a proposal to provide salary cap relief if a star player suffers a long-term injury in a Test or State of Origin was endorsed at Tuesday’s CEOs conference.
www.nrl.com
This article also uses the wording
'salary cap exemption' meaning a club can spend that money on a replacement player and that money won't count in the salary cap.... but it doesn't explicitly say the NRL will pay the club that amount of money.
No idea what that means, but it appears to leave open the possibility of a pauper club (or one owned by a cheapskate) to simply say, 'nah that's OK we'll carry on with what we have', rather than fork out money from the club's pocket.