I had an award ticket in October redeemed with UA miles with only the first, short (YVR-SEA) portion on AC (and in Y since it was a single class flight). The rest, SFO-NRT, was in C on NH. No problem at all using my two MLL passes that came via my CIBC AP CC. I was expecting some pushback, TBH, since I had used UA miles rather than an AP redemption but no issues whatsoever.