iPad Doc connector: is it possible to using the camera connection kit while charging the ipad
I haven't yet verified this with the MFi documentation.  However, it sounds like Matt B. is correct in the sense that you can't be both a USB host and a USB client at the same time and charging means you're acting as a client so host functionality should stop.  

Other pins such as iPod controls, audio, video, etc may remain operable still which charging since they don't use USB.