If you arrive on UA Metal you need to be either in Polaris or have GS status.
Is Polaris still sufficient to gain access? Lufthansa's website currently states: "
Access only for: Lufthansa First Class and Business Class passengers as well as Lufthansa status customers arriving on an intercontinental Lufthansa flight (LH 401 - LH 799); HON Circle member arriving on a flight operated by Lufthansa, Swiss or Austrian; United Airlines Global Services Card members arriving on a flight operated by United; First Class passengers arriving on a flight operated by Air China." But, there is no mention of United Polaris.