Hi Mars,
We have done a few procedures now of grafting into donor scars. The size of the donor scar will determine how many grafts it will take to cover it enough so that you cannot see the linear scar. It certainly can be done.
I've seen some of our strip scars be almost undetectible - quite difficult to find. I imagine if they wanted to they could FUE grafts so they can have the option to shave with #1 or zero guard. However, these patients are not bothered with their donor scars and would rather save the donor supply for the top of their head.