They way you think of the two is a bit like this:
Gutloading: Insects like crickets have a really horrible ratio of nutrients, so when you give them a well rounded diet of fresh veggies/fruit and commercial gutloads like Cricket Crack, Superload, Dinofuel, etc., you round out and enhance the nutritional value of the insects.
Supplements: Since these consist of minerals like calcium, supplementing your insects with calcium is like drinking that glass of milk after a healthy meal, you round out the good vitamins with good minerals. Crickets for example have a ratio of calcium to phosphorous of about 1:3, where as it needs to be in an almost 1:1 ratio in the body for bones to absorb calcium properly. So by dusting crickets with calcium, you raise up the level of calcium to phosphorous and you make it more appropriate.
So definitely learn about both and apply both techniques to your husbandry. They are both very important in trying to create the most well-rounded diet for your chameleon.
