Exactly. This is what frequency managers do, they manage freq's for events. Most of our concert works are part of a larger event where there are loads of wireless' around, and therefore we have to "check in" before turning anything on or setting freqs. This includes not just video of course, but operations, military, law enforcement, etc, etc.
You definitely don't want to be caught turning on a device in a managed area that isn't part of the plotted allotment.
*can* you use a US device in Scotland? In terms of radio use, most probably. But getting caught isn't cool. We got caught doing this several years ago at the Water Fest in Stockholm. They threatened to confiscate our rack of wireless receivers. :-(

Here's a funny (maybe not...) case in point.

http://gizmodo.com/gadgets/portable-...ban-176053.php

Spot on...
 

Spot is exactly right. If you are working in a highly congested frequency area, or a special event you have to clear with the frequency manager. Example: conventions, Olympics, etc. If you are far out in the boonies overseas where there are no competing radio transmissions, it will probably be OK.