Is It Normal for a Tummy Tuck Incision to Be Splitting Open?

 Unfortunately this is a complication of the procedure and is referred to as an incisional dehiscence which can have multiple causes including poor nutrition post-op, infection, smoking and increased tension. If you can, you may want to increase your oral protein intake to 60 gm per day with a protein supplement. Look out for infection and protect the incision by keeping slightly flexed at the waist. Other things that can contribute to it are smoking and even second hand smoke, as well as underlying fluid collections. 
Good luck
Dr. Trussler

This is not normal. You need to express your concern to your surgeon and if they don't address it, please seek the advice of another surgeon who can. Best of luck.

Smokers are definitely more prone to this problem. If the wound is open, you should be performing some form of wound care. A separation of 1-3 mm may be of little concern whereas a 1 cm opening is a different matter and may require more agressive treatment.

I am sorry to hear about the complication you are experiencing.  Superficial separation of the incision line is a known complication after tummy tuck surgery.   Close follow up with your plastic surgeon will be in your best interests; sometimes removal of a exposed suture and/or removal of any unhealthy tissue will expedite healing. Otherwise, wound care regimens will differ from one plastic surgeon to another.  Generally, this will involve application of some type of sterile dressing ( in my practice I use a non-stick dressing covered by a sterile dressing). You should have peace of mind that these types of wound healing problems generally go on to heal over the course of the next several weeks,  without long-term sequelae. Also important to concentrate on a healthy diet,  including good protein source. Occasionally, in the event of a wider scar, scar revision surgery may be helpful down the line.  Best wishes. 

The wound dehesince post surgery is unusual an needs treatment. You needto discus your concern with your doctor and if not happy with your doctors care,seek another plastic surgeon. There are many reasons for the wound opening including poor nutritient, smoking, too tight closure,infection .

Your abdominal incision really should not be open.  If you can find another surgeon in your area who is willing to assist you with wound care as the incision closes, that would be optimal.  If a very large segment is open, you may need to have this cleaned and closed in the operating room.  If you are experiencing any fevers or drainage, you should either call your initial surgeon or see another surgeon right away.  Good luck, /nsn.

Strictly speaking, separation of a surgical incision is never "normal" but is not uncommon. The fact that it is associated with redness means that it is inflammed and may be infected.
Your surgeon should make clear to you what he/she thinks is going on and how it needs to be managed.