I had an AP with my son and had an emergency c/s.
I did ask OB about this exact question when I found out my placenta was anterior and he said that it generally is not a problem because it's usually high enough that it's not near the incision (which is made very low - around the top of your pubic hairline).
He said if there was any doubt they would do an u/s in the OR to double check where it was.
When I ended up with the caesar though it was fine and well out of the way.