Is it possible to use back hair and neck hair for transplant to crown? (FUE)

Would this back and neck hair be suitable to transplant as a density filler in the crown of the head? I've waxed my back/neck for several years, so I don't have much hair there. What I do have left, I'd like to use to add density to crown. Trying not to take more donor hair from sides/back of head. Also, as I have transplanted hair to the crown in the past, is there anything harmful about more densely packing in more hair next to other transplanted hairs from past transplants?