You may use the AirPort Admin Utility to confirm whether a USB printer is recognized by an AirPort Express or AirPort Extreme Base Station.
Notes:
Use these steps to verify that the base station recognizes your printer:
The printer appears at the bottom of the Show Summary window if it is connected and recognized, like this:
If the printer is not listed here, try disconnecting the cables and reconnecting. Close the summary window, and repeat the steps above so that AirPort Admin Utility updates its listing.