I can only provide my experience. I've traveled to Coz, and FL, and never had to get a new VIP to get a fill on a pony. Most places understand the need to empty the tank for travel. They did a quick flashlight inspection just to see if the tank was clean, or at least in FL they did. In Coz, I have no idea. I just dropped the tank off with the DiveOp, and the next day it was back full.
Upon returning home, I also had no issues. They just filled it up!
Dive Ops can Absolutely charge you for a vis on an empty tank, unless it is brand new. Sometimes they even charge in that case as they are pissed off about folks purchasing online. I know folks at our local dive Op, and they have never been jerks about this, but it is within their right to charge.