Should I be concerned with this rash? (photos)

The rash that your photographs demonstrate could be any one of a number of possibilities.  In my opinion, the most likely possibility is that the rash is a sign of infection and the redness on your abdomen is referred to as cellulitis.  At this juncture, it is absolutely mandatory that you call your plastic surgeon.  If he or she is unavailable and has no backup plastic surgeon on call, then I recommend going directly to an emergency room.  Early treatment is mandatory.

Unfortunately, these happen from time
to time and it is usually difficult to elucidate the cause be it drug or contact
(or stress). If the surgeon is sure it is an allergic reaction, a Medrol dose
pack and topical steroid cream can significantly limit the reaction and help
the itching, which can drive you mad. It will go away with time so hang in
there.

It looks as though you have an allergic reaction either to the topical prepped or two and adhesives. It's also possible you have an allergy to antibiotics if you're taking them. In any event you should report this to your surgeon.