Theoretically I'm pretty sure that would be able to work. However, you've got to bear in mind that the iPad simply may not be able to supply enough current to reliably operate such an old keyboard as well as the iMate adapter. I'd be inclined, myself, to use one of those microcontroller-based ADB -> USBHID convertors, and supply (if you're clever, what you could do here is use the SE's original mains plug at the back, to connect to both an iPad charger (hell, you could whip up a custom charger circuit for it yourself)), and also a 5v supply so you can power other things - hell, make it one 5V 3A supply and you've got enough to charge the iPad at 1100mA and power a few USB toys!
That said, I doubt there's anything to be lost by trying
