Hair Transplant for grey donor hair is a Challenging job. yes it is possible &results are equivalent to black hair donor . Both FUE &FUT can be done but FUE is a better choice. FUT can be done if stereo microscopes are used for follicle dissection.
Before going for extraction of follicle we colour the grey hair so that they becomes clearly visible thought FUE is preferred for 100% grey hair. But if donor Area is limited we do FUT also. Here are some images of grey hair grafts & immediately after implantation.
We keep grafts in plasma to provide them same biological atmosphere as in the body & also do PRP during the hair transplant procedure.
So, yes grey donor area is more demanding as compare to normal black hair. But will get same results after hair transplant in hands of a qualified doctor.