I have the keyboard dock and the iPad1 with the Apple case. Love the case, but the iPad is a real tight fit and you can't get it into the keyboard dock supporting 'slot' with the case on. I think this is going to be a problem with most/all cases, because the iPad is (inevitably) a tight fit in the supporting slot in order to make it secure.
Having posted this once before in response to a similar question, there was a response from a Forum member who had come across a case that could be used with the dock - I can't remember the details but perhaps they'll post again.
I bought a Bluetooth keyboard in the end.....
Tim
Scotland