Yes, if there is a stored scan you won't need document check and can do OLCI more easily. I can't really say for sure why they let you print a BP via the desktop browser without the scan but they don't let you do it in the app. Probably two different IT departments that don't talk.

FWIW the UA app is an utter pain with scanning the passport, I couldn't get it to work and had to ultimately use a kiosk at the airport, but just the first time flying on that passport.