Why not?

NuWal isn't paper. It's a fiberglass mat done in a 3 step process. I don't know that you can sand down the seams, it's not paper, it's not joint compound, it's fiberglass. If you have an outlet, take the cover off and then you might see the fiberglass. Or you can gently pull (at the outlet) to see if the rubber compound is there. That would be a way to test. You can fill in the dents over top, that wouldn't be a problem, but I don't think I'd sand directly on the seams. How much did they overlap? You might get away with using joint compound feathering out from the overlap. A good flat paint will also take the noticeability out of it.