Chris Perkins has more than once mentioned Paizo employees who were members of his games in "The Dungeon Master Experience". And I don't mean just mentioned names of folks who happen to be Paizo employees, but saying, "So-and-So, from Paizo."
The RPG creative community is relatively small, and there's been quite a bit of movement back-and-forth between the companies. Pathfinder is essentially houseruled 3.5, which I imagine virtually all of the creative team at WotC is familiar with and even playing at times. As for Paizo, it's important to remember that their development of Pathfinder was not so much because of deep philosophical objections to 4e, but because of the restrictive GSL making it risky for them to base their business model on 4e adventures.
So on the creative side, I'm sure there's a lot of mutual admiration. On the business side, probably not so much.