Nice article by N. Gregory in the NY Times about immigration and the economics profession. He uses his own department (Harvard) to show just how open academic economics is to foreign talent. But it's not just Harvard.
Take my own department in the middle of nowhere. I've already written about its cosmopolitan composition here.
This year, we are hiring an assistant professor. The three finalists are Canadian, Portuguese, and Korean.
The only real barrier to entry in the academic economic market is ability to speak English.
I once worked in a university in Mexico. The Econ department had professors from the US, Guatemala, Spain, & Peru.
The barrier there was the ability to speak Spanish (though when they first hired me, I really was a terrible Spanish speaker).