My guess would be that reversing the servos would cause the AP to behave very badly when engaged. Think about it: AP thinks you need left roll input, it commands what it thinks is left roll and the plane rolls right. Well, now you need MORE left roll, so it tries harder. It will keep commanding "left" and getting "right" until either you or the AP decides to stop, or impact occurs. Same thing with up/down pitch.
I would hope it's smart enough to figure out that the servos are not doing what they are supposed to, and disconnect and complain about it.