It's hard to imagine an occupation against a population armed with millions of rifles capable of hitting a soldier at 500+ yards.
It's hard to imagine any well armed population being successfully occupied against it's will. Look at how much difficulty a small percentage of the population is causing in Iraq, and most of them aren't all that well trained.
As the Japanese Admiral noted when asked why Japan didn't ever try to land in the US, 'What are you crazy? Every one there owns a gun.'
The sharpshooter scenario though is very much like the English approach to the long bow. The real key to any such defense is that if the people all want the same thing, and all are willing to risk everything for it, they essentially don't need command and control. If the Shite's ever lose patience with the occupation, we will see that happen, and it won't be pretty.