Okay, I figured it out... turns out I was doing some contour rendering in other files, and when I created this file there was still a check beside "around all poly faces" in the contour rendering options, though contour rendering itself was solidly off in every area of maya.

So if I enabled contour rendering to access the options, unchecked my poly face option, then disabled contour rendering again, I don't get the warning and my anti-aliasing is peachy. Stupid mental ray.