Since they were still moving forward while gunning it in reverse the rudder would still operate normally. They generally have bow thrusters too. I have no idea whether they could have been operational with the broader power/engine failures but if they were available I'm sure they were being used as well.
The question is what is the velocity of the water moving over the rudder? If forward velocity and the current due to a reversing prop cancel, then the rudder can't do anything.
