The rudder damper system is (usually) designed to prevent excessive rudder deflection at high speeds in a mechanical flight control system. In a fly by wire system that is taken care of in software.
Yaw damper is designed to "damper" yaw movements not to limit rudder deflection. RTLU (Rudder Travel Limiting Unit) is there to limit mechanically the rudder deflection depending of A/C speed, this units (double) are driven by FAC's fonction of speed information from ADR's.