They should put him in the K9 Unit, he doesn't need a sense of smell then. In fact it would be an advantage if they gave him a Labrador
Now, being serious. This is rubbish. A cop doesn't need a sense of smell. A dui driver is usually observed driving in a certain manner and when he or she alights from the vehicle (in the US of course field sobriety tests are used) then there are plenty of indicators as to if a person has been drinking. A drug driver doesn't necessarily stink of anything either.
Now, it might be that he may miss the odd cannabis pinch as that stuff reeks, but big deal.
He should get his job back. This is a crock.
"Unbloodybreakable" DCI Gene Hunt, 2008