I Still Have Fat on my Stomach After my Tummy Tuck and Diastasys Repair?

If the fat is inside the abdomen (underneath the fascia, 'beer belly'), the surgeon can't reach or remove that fat and weight loss will be necessary.  Intraabdominal fat is especially bad since it is associated with heard disease and diabetes.

If the fat is outside the abdomen and can be 'pinched', it may be accessible to liposuction. Often it's not possible to do all the liposuction the patient might need at the same time as the tummy tuck since that increases the risk of the surgery.  

In those cases, liposuction is possible, usually several months after the tummy tuck has healed.

fat after abdominoplasty or tummy tuck

as noted in the other answers ,  fat within the belly needs to respond to diet and exercise.

fat under the skin can undergo additional liposuction for contouring.

I'm not quite sure what you mean by "hard" fat.  I don't get too crazy with the fat over the abdomen during a tummy tuck because I worry about damaging the blood supply to the skin.  I tell my patients that, if there is still some fat in the area after their tummy tuck, we can do a little corrective liposuction at a later time.  That may be what you will need.