Well, from what I can tell GM had these air flow indicators on the early LH8 motors (2008-2009) and then sometime mid-year of 2009 they redesigned the airbox and eliminated the airflow indicator. Guess this makes the early LH8's even more rare.
Here's a pic of the original first design... take notice of parts #4 and #5.
My truck was built in May 2009 and and doesn't have the air flow indicator.
I would think that anyone with the LH8 or LH9 could add this air flow indicator simply by drilling a hole in the air box and adding the grommet and air flow indicator. I suspect that the air flow indicator is a visual indicator the helps you determine when it's time to replace your stock air filter or clean your K&N filter.