1) Put your LH number into the system, and once you get to the gate, after it seems like the manifest has been printed, a la boarding will start soon, then go up to the gate agent and get it changed to your UA card. That way all the *G benefits are honored.

2) I don't know about LH, but BD gave me an email that I printed and showed to everyone wherever I went, and it worked out fine for me. YMMV.