Which is why I recommended the diode. 
Sure, and with the diode, no special treatment is needed for the control output - just set it to output and LOW to make it active.
Can't a backfeed happen even with the diode, though? Suppose the controlled device is on, the controller is off. Current will flow from the pull up resistor on the controlled device, through the diode, then through the protection diode in the controller, to it's Vdd (now at ground potential)? At least, there is some risk that turning off the controller would cause an activation because it pulls enough current through the pull up resistor to register as a LOW to the controlled device...
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