This is from a really old version of the rules, because I'm too lazy to download a new one. I know the rule hasn't changed; some of the language of rules numbers may have:
504.4. If you control multiple face-down spells on the stack or face-down permanents in play, you must ensure at all times that your face-down spells and permanents can be easily differentiated from each other. This includes, but is not limited to, knowing the order spells were played, the order that face-down permanents came into play, which creature attacked last turn, and any other differences between face-down spells or permanents. Common methods for distinguishing between face-down objects include using counters or dice to mark the different objects, or clearly placing those objects in order on the table.
So, the answer to your question is "no."
Well given the wording it seems like you could shuffle your face down creatures so your opponent didn't know which was which, but if your opponent asked which was which you would have to tell them. Is that right?