Human probiotics are okay. You want one with a variety of bacteria, as the diet and the intestines themselves will encourage some bacteria as opposed to others, and you can't know beforehand which ones that will be. So you want a wide variety of bacteria, and lots of them.
The best thing to do for food allergies is to reduce the variety of possible allergens the dog is receiving, so feed a diet that is appropriate for dogs, meaning giving one type of meat (beef, chicken, etc, including bone, raw or cooked), fish oil, and the probiotic or yogurt. If the dog is allergic to one type of meat, avoid that one. Avoid all commercial food, treats, etc, until the allergy clears, and then add foods back into the diet one by one, until you find what causes the reaction.