I toured the GDMBR a couple of years ago on a bike with V brakes. I had no problems. As mentioned further up, there are no real MTB sections, ok maybe Fleecer Ridge, but most walk the worst of that.
I started with new wheels.
I carryed spare pads, but didn't need to change them!
The only real problem I see with them compared to disc's if you you were to break a spoke/buckle a wheel, this could render the brake unusable, not the case with discs.
Cheers from a great New Zealand summer