I don't agree that Boeing had a split Rudder on the B727 so they could have two yaw dampers (or dampeners as some of our southern friends called them)
The 757 /767 has two yaw dampers but does not have a split rudder.
I think it was more for redundancy of having two separate powered rudders on the 727.
I do agree, after seven years of flying that lovely Aircraft that you don't want to go above 25000 feet without at least one Yaw Damper and without any it had very unforgiving dutch roll.