COGs are blinded from constant work in dark caves with super bright lava. It is almost impossible for them to spot the player unless they are fired upon, or damaged in any other way. If that happens, they will charge in the direction of incoming fire and fight back! So be careful!
Normally, dispensers only show the item count from storage. (Whatever item it's supposed to pull, it shows the count you have in storage.) It will not show the count of however many items are loaded in the dispenser.