He's full of baloney, Rob.
Many states still use salt on their roads to improve traction.
And while it's true that the salt does speed up the corrosion process, it does not void any manufacturer's warranty that we know of. That doesn't mean that they'll fix the car if it rusts. It only means they'll fix any part of the car that actually rusts through - where rust makes an actual hole right through the body. So if you expect to take advantage of the rust-through warranty, Rob, at the first sign of rust, you might have to start sprinkling salt on those spots on a daily basis. His Social Security number and home address are available upon request.