Yes. Users have reported that USB keyboards work with the iPad. To connect a USB keyboard to the iPad you must have the Camera Connection Kit accessory.
The Camera Connection Kit adapters plug into the Apple 30-pin dock connector port. One of the adapters has a USB port that is officially advertised as a way to connect your digital camera directly to the iPad. Connecting a USB keyboard to the adapter works.
It's possible some keyboards will not work. Apple officially does not support the use of the Camera Connection Kit for anything but digital cameras.