So adding the following to "Extra Parameters" on each docker will allow you to offload the syslog to the IP and port specified. Make sure you change the value of tag to something notable so you can sort in Graylog and your IP of course.
--log-driver=syslog --log-opt tag="radarr" --log-opt syslog-address=udp://192.168.1.55:514
If you are using TCP on your input you can use:
--log-driver=syslog --log-opt tag="radarr" --log-opt syslog-address=tcp://192.168.1.55:514