As the Gasman said, the kelp forests are found in the southern South Island, but can be pretty tricky to get to unless you are on a decent local boat, as the coast line around there can be pretty rugged. Stewart Island (NZ's 'third' major island, south of the South Island) has by far the best kelp forests, with clear but cold water that is home to seals, sea lions and you guessed it - White Pointers. I'm pretty sure they aren't commonly seen by divers (if at all) and you'd be really lucky (or unlucky) to see one. It certainly doesn't put anyone off, as there are plenty of other places around NZ where they can be found, so there's no drama attached to it.
I'm not sure about kelp forests around the Marlborough Sounds ( where the Mikhail Lermontov is) but another site for you to check out would be
www.divenewzealand.com which should give you details about all the good spots around there. The Lermontov is definately worth a few dives if you get the chance. She was a 155m long 25m wide luxury cruise liner, and in 1986 sunk onto a sandy and silty bottom in 37m of water, and has a real ghostly feel due to the sometimes reduced viz. There are also caves in the area (look up Riwaka Srings, Pupu Springs, and Riwaka Resurgence).
I'd love to answer some more questions as well, so keep 'em comin'!
By the way, where are you situated Gasman?