We flew to Jamaica on US for our Honeymoon a few years ago. We had used AmEx points for first class tickets. While hanging out near the gate desk for the flight to board, we saw several young couples walk up and explain that they were on their honeymoon and asking about an upgrade to First due to their special day. The Gate Agents response each time was ‘sorry, everyone on this flight is on their honeymoon’.

Sure enough at least in the 12 seats in First, all 6 couples were on their honeymoon.

Good luck in never hurts to ask.