Yes, Campden tablets (metabisulfite salt) do add sulfate to your water. However considering the typically low dosing of that compound, you are only added a couple ppm sulfate to the water. So it shouldn't be a concern. PS: they also add a couple ppm of chloride too! Read the Water Knowledge page on the Bru'n Water website to understand the reactions with metabisulfite and daughter products.
AJ and I say that boiling for chloramine removal is ineffective...but only in the fact that it takes a LOT of energy to drive off chloramine. It works, but its not a good use of your time or resources. Chloramine is far less volatile than chlorine gas and it is harder to drive out of the water. Given the ease with which metabisulfite can remove chloramine and the fact that it DOES NOT result in any residual sulfite in your beer, you would be wise to employ that treatment in most cases.