hi, you have given a very good description of your scar, the reason the scars look that way is because the skin in the region of the scar has got very few adnexal (Sweat glands, Oil glands, hair follicles) structures and below the top layer of skin is just scar tissue with fewer blood vessels (compared to the normal skin).
the way dermaroller works is by making micro-punctures in the skin with the intention of stimulating deposition of new collagen and other good stuff that improves the quality of the skin. the cells that make the collagen etc are however deficient in scar tissue especially if they are big (like your scars) I would therefore think that it is highly unlikely that you would get any benefit from the procedure
hope this helps
warm regards
dr prashant