Now that my BB is unlocked, do I still need to remove the vendor.xml file when to OS versions not released by my carrier?
Yes. Most phones worldwide aren't locked in the first place; the US is unique that way.
The vendor.xml file is there to verify that the country code of your phone (which identifies both the country and carrier for which it was originally manufactured) matches what that of the carrier that released it. From your homescreen, if you press ALT+EACE or ALT+SHIFT+H a status screen will pop up that will display your country code. It's hard coded onto your phone and (for the most part) can't be changed.
So, whether or not your BlackBerry is locked or unlocked doesn't change your need to delete the vendor.xml file when loading OSs from carriers other than the one who originally sold your phone.
Posted from my CrackBerry at wapforums.crackberry.com