Smitty does not execute the command specified against "restart_command" option in the agent.yml file if the command specified has command line arguments!
So, /etc/init.d/twemproxy restart won't work assuming there is an init script present for twemproxy!
Following is a sample log:
Cannot restart twemproxy. output: . error: exec: "/etc/init.d/twemproxy restart": stat /etc/init.d/twemproxy restart: no such file or directory