We don't know the second carrier, so there is no way to know if there is an agreement. The OP claims it is DL, which it isn't. It's likely either Korean or China Eastern/Shanghai. While there might be an agreement with Korean (I really can't tell for sure) there appears to absolutely be no agreement with China Eastern/Shanghai. ANA can be ticketed through DL, but there's no codeshare, so no DL flight #. Same with KLM and AF.