Was at the store today and asked the dude behind the counter to put a Canon grip on a 5D2. There was a visible gap (~.5mm) between the body and the grip...is that normal? I ensured that he removed the rubber cover on the bottom port.

Mine doesn't have any space, but it is also locked onto the body due to the previous user over tightening the thumb wheel and stripping the plastic gear in the process. It's possible that either the person didn't tighten the grip quite enough or there is some sample variation from grip to grip that cause some to fit better than others.

That's normal. No worries.