Is it true that there is no need for a women to exercise after having
a hesterectomy because the stomach muscles are gone and the fatty
tissue can only be removed thru surgery?

A hysterectomy does not remove the abdominal muscles. A hysterectomy
removes the uterus, an organ which is deep within the abdomen.

It might be the other way round. 

A hysterectomy could (and usually does) cause a change in the hormonal
balance, which in turn could lead to weight gain.

In addition, after every abdominal surgery, it takes time for the
muscles to heal and for the patient to be able to use them again for
exercise.

No, it's not true.

- Hammer