I'm pretty sure that it's not possible within Apples guidelines/rules. At least I can't think of any other reason why the rather obvious IT tool is missing from the App Store.
This may not help you much (unless you happen to have an Android device), but I have an app on my Android phone call Wifi Analyzer, which is exactly what you are looking for.
Channels 1,6 or 11 are recommended to avoid interference. You will probably need hardware other than the iPad to see the channels in use by your neighbors. Netstumbler on a PC/Mac for example.