Using the iPad dock connector to connect cameras - airplane mode - no WiFi
Using the iPad camera connector with the USB port seems to work with certain items (headsets, etc.) that aren't cameras, leading me to believe that there is a full USB hardware implementation in there but there simply aren't any drivers. If this is true, you could get a USB Ethernet dongle, write iPad drivers for it in your camera-viewing app, and use Ethernet to connect to your cameras. I doubt that would get on the App Store, but that's not a problem, given that you will be using the Enterprise distribution method. This might also preclude charging the iPad while it is connected, so you may have to design and manufacture your own power-and-ethernet dongle.