Do I need ductwork for a through-wall exhaust fan?
Other than the electrical issues I would not be worried about duct work two much you are pulling the heat out of the fridge so that should if anything pull air through if you are concerned a 2x 4 or 2x6 wedged in the cavity would stop almost all the air flow. I have used listed window fans for air movement through living spaces but never a fan not in an enclosure that is plugged in.