Is A Gullibility Test Ethical?

Linksprocket are carrying an interesting post entitled US Army "Scams" Service Members to Test Their Spam Gullibility

Now isn't this a case of Double Gullibility? What are the army famous for? Well- giving orders and expecting them to be obeyed without question would come pretty close to top of the list. So what did the creators of this little scheme expect?

Of course the people they sent the message would carry out the orders especially since it was passed off as one of the most trusted divisions of army welfare.

Is it ethical to dupe people you have trained to trust your instructions?