It could be yes, but every time I pass through there it is fully open and working. Sometimes when I get to the front nobody is on the "secret" line and they will open up a barrier between the lanes and invite me over.

I'd say 90% of the time it's running at full capacity with a line full of people waiting. Those people don't get pulled off the main line, they came in through another entrance from the ticketing area (if you look carefully you can see through the door back into the ticketing area). So I'm fairly certain it's not just an overflow area, there's some other trick to it.