Ooo. That's scary. I would consider another contractor quite frankly. While no expert by any means, my father in-law is. In fact, he is adding a 2,000 sq.ft. second story to our home. Apparently, the name of the game is not so much vapor barrior as is 'air movement'. House wrap prevents air from moving from inside, to the outside, and vice versa. One of the benefits in the process is that of moisture control. That being said, if a house is too tightly sealed, you can have moisture actually trapped inside where you don't want it. Fortunately, most windows/doors are where the majority of 'leaks' occur (by default), so usually that's not a problem.
My advice is that you do definately want to use house wrap (brand is probably not the end all) to control your air movement. We ended up using Tyvek since that's what Home Depot had, but would have used anything else. The key is to make sure your contractor puts it on in one piece around the entire house as he's able. Then the windows/doors are cut out later. A special tape is used to seal ALL of the seams, tears, etc.
P.S. Again, no expert. Just passing on what I've learned.