Nate didn't know what he was up against when he fought Rory. The mixture of kicks and wrestling really threw Nate off his game and he wasn't anywhere near as aggressive as we're used to seeing him.
Nick, however, would know what to expect and properly train for it. Could he stop Rory even with the knowledge of knowing Rory's skillset? I say yes, while also still realizing that Rory is the toughest opponent possible for Nick Diaz at Welterweight.
Rory uses his wrestling to rag doll people around, not to put them on the ground and either lay on them or look for submissions. Rory's wrestling is apart of his striking, as weird as that sounds, and Nick's constant forward movement would leave him vulnerable to Rory's wrestling.
That said, I still think Nick finds a way to win against anyone who actually goes in there to fight, and Rory, to his credit, is someone who fights. Plus, you have to imagine this would be a 5 rounder and since there's no way Rory ever finishes Nick, you have to give Nick a big advantage in the later rounds since we know he can last there and we haven't seen Rory go past 3 rounds.