My guess is that there is no actual job called a dog food taster.  But, the dog food companies go out of their way to add spices, cheeses, ingredients that taste good, so dogs will like the food better.  I tried my dog's food once and it was pretty good, as weird as that sounds.  I wouldn't be surprised of the people making the food and deciding on the final ingredients popped one in their mouth to see what it tastes like...