Is it possible to have SMP on top of the recipient area after an FUE transplant to add more density?

Scalp Micropigmentation SMP can be a great adjunct after hair transplant surgery to add the look of fullness.  You can have SMP after all your scars have healed.  It would be up to the doctor as each doctor has their own criteria and comfort level. 

The two techniques can be combined as the offer different benefits. The FUE natural hair growth and scalp pigmentation adding the look of fullness or density. Depending on the plan and your hair loss pattern they can be used with a shaved look or if your hair is diffused thinning. Longer hair needs enough native hair to ensure the pigment looks natural though. Too low a hair density will not blend and the pigment stand out for what it is. 

Yes, micropigmentation can be done to make hair look thicker after transplantation.  You'll need to wait for the hair to grow in before he pigmentation is done.