Well they can do what they are good at which is marketing or sales, but since the product is not sufficiently done, what are they gonna market? in addition to that the whole company is in stealth mode anyway.
We want to get as many users as possible so we can get content (if the application really depends on userbase) or be profitable as soon as possible (in the case where we're building a business-oriented product that aims straight for revenue with solid business model). But in both cases, I still don't see how they are going to be useful at very early stage.
This person could also work on developing relationships with people who could become your future evangelists. Who do you have lined up to talk about how your product is the greatest thing since sliced bread?