It might indeed. Do you mean that it could use my NAS as the primary storage, like Time Machine can? Or do you mean that it backs up my NAS to their cloud? It's hard to tell which of those it is, based on their page.

The former is useful to me, the latter is not. If the former, I wonder if their free version would allow that (i.e., they only would charge a subscription for their cloud storage). Can't easily tell from looking at their web site.