Officially? Only if they plan on buying that one... From that Training PDF:
"Customers who purchase iPhone will leave the store with a sealed box. The box is not to be opened in-store."
"DO NOT open up boxes for a customer to view the device, as the device is considered used once the box has been opened."
Now, that's the "official" stance... Whether or not they adhere to that is another story... But I sure as hell don't want to buy one in an already opened box.
Probably since they have demo units available, no need to crack the box just to make sure your iPhone looks like all the other iPhones they'll have out for potential buyers to play with.