I can bet that a controller at one of the big places in Europe could easily come to the US and train and be a perfectly usable body in the operations room and vice versa.
This is happening as we type, fine people from Australia have found the way to our Ops Room
http://www.eurocontrol.int/muac/publ.../homepage.html , have qualified and form part of the control staff. They remain the exception though. We are still looking for people though, just like most ANSP's.