Kang: Can two players control the same unique cards while they are in different game areas?

Yes. Cards in one game area cannot affect other game areas, so a unique card in one game area places no limitations on the others. When players combine game areas, they must discard copies of unique cards until only one of each remains in that game area. If the players cannot agree which one to discard, the first player decides.

-The Once and Future Kang rulebook