seats are predefined UA or LH seats on such transatlantic flights.

if the flight is booked as a LH flight number you don't get status bonus nor 'true-flier-bonus' into your UA Mileage Plus account. Only class status (25% in paid business) if appropiate is added. But you could upgrade such a flight with UA miles on 'selected' fares (same fare rules as otherwise on UA).

You can't upgrade with any miles/vouchers if the flight is booked as a UA-code-share-flight-number with LH being the carrier, but you than would earn status bonus miles and true-flier-miles.