In theory, yes.
If you have anaphylactic allergy to casein i'd steer clear of whey because you can't be certain that it's 100% free of casein.
And if some whey products are, others may not be. So its russian roulette. Incidentally, tuna fish packed in water is routinely packed in a little cow's milk, watch out. Tuna packed in oil is safe. 92% of cow' milk allergic persons are also allergic to goat's milk.