As the title says, Swap and Stun abilities (such as the one from triceratops gen 2, tenontosaurus or iguanodon) do not work with swapped-in dinos when they are swapped at the same time. This has been tested in friendly battles, swapping Dracorex gen 2 and triceratops gen 2 at the same time for several times, and did not work a single one. This could be that the stunning effect just didn’t happen but my friend reported the same results so it’s statistically very unlikely.
This is important because this method would be currently the only theoretical way to counter or avoid the dreaded swap and defense shattering rampage ability from the Dracorex gen 2.