The thermodynamic efficiency of the heat pump is higher the higher the temperature of the cold side, so at least in places where the outside temperature is warmer than the fridge or freezer this wouldn't be a win. This is why you can improve the performance of a heat pump by having the outside circuit run under the ground where the temperature is warmer.

There's also the point that the fridge/freezer is already a heat pump dumping its heat into your house.