You could tint your fondant the basic background color of the cammo, then tint more fondant the other colors. Cut out random pieces and lay them on top of the rolled out background color and then roll it with a rolling pin to cause it to meld together and become a sheet of cammo print.
I'd practice on a smaller piece to see how it works since you won't be able to re-roll the fondant without muddying the colors.
I've used this technique to make fall leaves with changing colors.
I tinted different colors of fondant, broke off small pieces and set side by side (randomly), then rolled them together. Check my pics for the Lego Army cake. I will try to attach a picture of what I did.