What about the reverse, is it okay to use animal shampoo that was tested on humans? Or even human shampoo that was tested on humans? I mean lots of pet foods (cat foods especially) are taste-tested by humans, since humans can give a more subjective view not only of the taste itself but how that taste can be improved (ie. meatier, sweeter, better aftertaste, etc.) -- whereas with testing on a cat we can only hope to deduce the cat's actual view of the food from its behavior in the test (it ignores the food, eats the food hesitantly, eats the food with great vigor, etc.) The same is true for other animal / pet products.
And many products, like medicinal drugs, go through a whole process where they are first tested on animals and then (if deemed 'safe') tested on humans before seeking FDA approval. Some people make a career out of testing these non-approved drugs, sometimes with dire consequences, do a news search on the internet for more info.