If you connect an all-in-one printer/scanner/fax/copier type device to the USB port of an Airport base station, you will only be able to use the printing functionality of the all-in-one from a computer. This is the same regardless whether it is the older 802.11g Airport Extreme, the newer 802.11n Airport Extreme variants, the Airport Express and even the new Time Capsule.
It is not possible to use the scanning function of any all-in-one printer connected to the USB port of an Airport base station – and this limitation applies to all makes and models of all-in-one printers.
You will not be able to use the scanning functionality unless the all-in-one is connected directly to the computer.
Some all-in-ones are not compatible with the Airport base station and therefore no functions will be available.
Also you can not connect an USB scanner to the USB port of an Airport base station either.
From KB-article The USB port is for connecting a printer, not for other devices.
The key question that some are asking is, can you connect a scanner or an all-in-one to the 802.11n Airport Extreme Base Station?
On this page on the new base station it is quite clear that you can plug in a USB printer or a USB hard drive, it never mentions a scanner, which to me is pretty obvious that you can’t plug in a scanner.
It also says
AirPort Extreme and the Mac- and PC-compatible Bonjour networking technology let everyone in the house, office, or classroom take advantage of one centrally available printer.
In the same way as the old base station it relies on Bonjour for printing and Bonjour doesn’t support network scanning.
So can you use a USB scanner or the scanning capability of an all-in-one with an Airport base station, the answer is a resounding no.