Unless in came as an option from the factory, it is illegal (unless it meets ADR's of course).
VS2 came with CF bonnets from factory and as such are legal to use on all 34gtr's. An agument could be made for the legality of a guinuine nismo Z-tune bonnet as there was a z-tune registered in Australia. All other z-tune style bonnets are illegal for street use.
In saying that, i haven't heard of anyone been pinged for a well manufactued, colour matched z-tune replica. If you do end up getting one, just make sure your insurace company know's about it as it could void some policy's.
EDIT: just remembered you asked about mine a few weeks ago - i haven't had a problem with police since i put it on there...but i've never been pulled over in the gtr either :-)