Not necessarily. What if your app comes with a widget (or tile for Windows Phone apps) that tells you all the information you need. I'd have that visible at all times and would never need to open the app itself.
But I would assume that if you have a widget docked, then you are likely getting some use of it, and if not, you will undock it (and maybe also delete it).
So there is still a level of usage you could measure from widgets, though maybe not quite as meaningful as that you get from regular apps.