The short answer is yes if you want the fridge to be efficient. If you dont the heat exchanger fins at the back will, on a warm day, not be able to get rid of the heat.
These 3 way fridges are designed to operate with the rear of the fridge in a free moving flow of air.
Don't confuse heat vents with flue vents. they are not the same thing.
cledlyn, January 2009