I feel like I can add something to this thread. Me and my wife were booked from JFK to DEL for a return trip on deeply discounted Etihad in 2011 (I think that was a disaster of Etihad IT back in August or Sept 2011 for a day or two) and we were to get those flights credited to AA. Principal reason of why went to India was to get my wife's visa renewed. But there was a delay in visa-processing and my wife couldn't take the flight back (while I could). So I checked her in all the way on the return journey, and got the seat next to me free in all 3 segments (DEL to AUH, AUH to MAN, MAN to JFK). Even though I had checked her in, and got the boarding passes for all three segments - I expected that I wouldn't get any mileage for her.

Long story short, I got credit for both of us. However it could be due to the fact that credit was processed manually (In a long period of time) due to problems with Etihad crediting system. They had not even posted credit for me, so I had to request partner credit using their online system and since I was doing that I just did the same for my wife as well. When they requested boarding passes, I sent them those that I had. While this is not a case similar to UA posting on UA when you don't fly, but its' like LH posting credit to UA because someone booked and flew (or didn't) LH.

I think it was just luck though.