I just replied in the one Skype thread, but I guess I replied to 'has anyone used this' specifically.
WiFi follows the same standard I believe, independent of country. I've had friends from Britain, South Africa, and other countries get on wireless networks here with their foreign laptops and it's worked fine. Odds are, using a US Moto Droid to access WiFi, whether for Skype service via Nimbuzz or anything else should work fine.