If you use the NRaas Traveler mod to move, nothing happens to the Uni World sims and their relationships to yours. If you use NRaas Porter, you are essentially starting a new game with your existing local sims so the Uni World sims will be gone and replaced by new versions of the same sims on the next visit, thus no relationships.
For a move the EA way without the mods, I think it works the same as Traveler in this regard. The foreign worlds should stay intact, but I'm not entirely sure about that. Try it on a Save As copy of the game and if it doesn't work as expected you can always revert gameplay to before the move happened.
