How unlikely is it for a experienced hair transplant surgeon to extract (FUT) hair from a non-safe donor area?

It would be very unlikely that an experienced surgeon at a reputable clinic would harvest from an unsafe area. There are many factors that can cause previously healthy grafted hairs to look less healthy - eg nutritional deficiency, thyroid issues, and potentially loss of nongrafted hairs in the same region leading to less density and the allusion of less healthy hair. I would suggest returning to your transplant surgeon for an in person evaluation - PRP treatments or oral treatments may help with your situation

It is pretty unlikely that a doctor harvest hair from a none safe donor area, but one thing is that the hair won’t fall out because of genetics and other thing would be thinning and that could happen everywhere, maybe you need a DHT blocker and there are different choices talk to your doctor to see what fits best for you