I called in. TOok a while to get an answer, but apparently there is no "normal" 6 digit confirmation code. There is a 4 digit confirmation code domestic, which maps to a 9 digit code international.
It is a big guess if this will work at checkin with United. This being said, this being Japan, if (1) the inbound plane from ORD is on time (yeah, I know, a big IF these days!) and (2) there is not too much chaos at immigration, then in theory I should have time to recheck. I have to get my luggage through customs anyway.
At least, the Web site now retrieves my reservation, so apparently I am all good to go. English help desk lady was pretty nice too. Might help me remember to fly ANA more