That is that the tickets will be 016 (ie UA) tickets.

After purchasing on UA, look at the reservation online at the UA website to extract the LH reservation numbers. Nobody besides you and UA cares about the UA confirmation numbers. You'll need the LH reservation numbers to check-in at the LH desk to get your LH boarding passes when flight time comes. It's going to be LH metal. If you want UA PQM, verify that you've purchased the appropriate fare class on LH.

I've done this a few times for LH flights like FRA-NUE. No big deal. Perfectly safe. I'd do it again.

Of course, I've never had anything serious happen to these flights besides the usual flight delays, if anything. If something simple happens, I might ask the LH people, using the LH reservation number. If something serious happens like the flight gets cancelled a few weeks in advance, and I get put on some weird alternate schedule that I can't deal with, I'd ask the UA people. I've purchased SQ flights through UA and then dealt with UA when SQ decided to cancel the flight.

I believe that your concerns are warranted still. I've purchased KL flights through CO, way back when they were partners. Somehow, KL had the wrong month of travel on my return ticket out of Africa and said that I had to talk to CO to get it resolved. I had to pick up the phone and speak to CO reps in New Jersey to get things cleared up so that I could get on the planned flight, and not be stuck in Africa for an additional month. You might want to have UA phone numbers handy just in case. Try to get a local office phone number, so that if you wind up phoning the USA from Russia, that you don't get stuck waiting forever on a telephone elevator music hold. With the local-USA-location-phone-numbers, you also want to keep track of the time zones to make sure that you're calling during normal business hours.