IME, the answer is yes. I use OLCI and Digital Key whenever I can. If I'm not already upgraded when I do OLCI, then I have been upgraded after that numerous times. The hint is you'll get a notification on your digital key device that you've been assigned a new room, and here's your new digital key.

Others on the forum have stated that the hotel(s) cannot change your room after you've selected it via OLCI, but that has not been my experience...