Onion powder is added in a minute amount to reduce the strong aroma of 100% beef.
That is simply an odd reason imo. How strong does beef smell? I would think the smell of meat is what would entice a dog to eat it?
I'd be more concerned about the addition of sodium nitrate...a chemical preservative.
Considering the ingredients, I'm guessing it would take less than an hour to prepare a large quantity yourself to freeze in small portions. No onions or preservatives necessary and at a fraction of the cost.