Can an app be on your device but not on any screen?
No... not permanently. It's possible you ran into this iOS 9 glitch, but the app should appear upon restart.


  Create a folder with all the apps you want to hide away. While the
  apps are still jiggling, drag the icon one page at a time until you
  get to a blank page then let go. Attempt to drag the icon one more
  page over from the blank page, then tap the home button.