Is it common practice to not have x-rays done when a doctor has decided you need an umbilical hernia surgery?

An umbilical hernia usually is diagnose during the physical examination, and  X rays or CT scans are not needed. Usually the treatment is done with a direct approach, to close the muscle defect.

It it not necessary to obtain any imaging studies to diagnose a small umbilical hernia.  In fact, it would be uncommon to get an x ray or CT scan for an umbilical hernia, as these can be diagnosed on physical examination. At the time of a tummy tuck, umbilical hernias may also be repaired. 

Umbilical hernias are diagnosed by clinical exam.  Therefore, no X ray or imaging study is necessary.  The repair is simple and can often be performed under local anesthesia.  Good luck.