crickets have a poor phosphorous to calcium ratio - meaning they are much higher in phosphorous than calcium. this is the opposite of what your chameleon needs. So we correct that by dusting with calcium and gutloading with nutritious stuff high in calcium and vitamins. So yes, if you offer crickets, dust then (lightly).
Some of the other commonly offered bugs need not be dusted though, such as butterworms, pheonix (soldier fly) maggots, some leaf eaters, terrestrial isopods, etc