Sorry, but this makes no sense. If you did it and you put it down you aren't going to be joining the military. Why bother wasting everyone's time, they don't want you and won't take you. If you were dumb enough to smoke pot, and aren't going to hide the fact, then you can't join the military. They rolled the dice on their career when they smoked that first joint.
Of course what % of active duty officers do you think actually did smoke pot and didn't write it down on their questionnaire.
Not sure why you claim that if the OP checks the box and explains that it was a one time thing (As long as that's the case) that he will not be allowed to join the military. The military has two classifications, Experimental, and Habitual, the OP falls under experimental, he will most likely not have an issue.
Now, the part in Bold is what bothers me, why would anyone advise someone to just "Hide the fact"
This is what nick4060 was talking about when he said roll the dice with your career. Getting caught later will be much worse.
As far as how many officers did not check the box when they should have, who knows, but there are plenty that end up leaving when it's discovered they lied.
Having a hard time understanding what your position is, you seem very much against smoking pot, but perfectly fine with not admitting it.