Would all abdominal hernias be discovered/repaired during a tummy tuck if there was no previous knowledge of one present?

It's certainly possible to find hernias during tummy tuck surgery, but it's possible for a hernia to go undetected.  It depends where the hernia is located, and what portion of the abdominal wall is visualized during the surgery.  There are different techniques to tummy tucks, and not all of them directly visualize the same amount of muscle wall.  Many of the visualized hernias are repaired with the plication of the muscle and rarely need additional reinforcement, but this is a judgement to be determined at the time of surgery.  Also, not all tummy tucks inlcude a muscle repair/plication.  Be sure to be fully informed by your surgeon as to what is included with your surgery.  Surgeons have some variations between what they do for their particular surgeries; that's why price is not always the best method to compare surgeons. 

It is possible to find a hernia or weakness in the abdominal wall during a TT. In the full-figured patients it is often difficult to feel a minor hernia or defect before surgery is if is small. It is also the routine to repair such a defect if it is found during the procedure. These are usually repaired with a rectus diastatis repair (suturing the rectus muscle fasciae together).However, if the hernia is around the umbilicus, extra measures are taken to assure an adequate repair.

Yes it is possible to discover an undiagnosed hernia. If it is found it should be repaired when possible. I also believe that there maybe an unknown hernia that is not identified with a tummy tuck, particularly when a tummy tuck is performed with liposuction. I hope this helps.