Cant be sure of that, However we do know that saltwater ICH for natural reef tanks is an issue.
If NSW from NZ waters happens to contain them which it may not, then at least we know we have covered the bad ones we know about for Reef tanks. Other parasites may survive 3 or 4 weeks but may be NZ parasites may not harm Reef tank inhabitants anyway.
It is purely theory, but I like it and know it definitely kills and removes some things as well as settling crap out also.
It is definitely beneficial to common Reef Tank Marine ICH. (As we know the cycle of this parasite. (Even if it only kills the majority).
If we just dumped it in and it had heaps of Theronts for example...our fish may get swarmed and find it difficult to get rid of.
If we leave for a term and the New NSW contains only a few...the fish should be able to cope and keep up immunity.