The most common allergy-causing ingredients in dog food are corn, soy and wheat. Most of the high quality, human grade ingredient dog foods, like Wellness, don't carry these ingredients. It's the cheaper foods that use corn especially.
Wellness is an excellent food. In fact, many allergic dogs do well on their whitefish and potato formula.
Here is a useful link from Flint River Ranch that compares their product to some of the others out there. It also has definitions of various ingredients: