This has nothing to do with DUNDI. You should have used Asterisk Support.
With -rx, you must use the actual name of the Asterisk executable (normally /usr/sbin/asterisk). The startup script only takes one parameter, so if you do it that way, you want restart without the gracefully. It will never do a graceful restart.
Why do you want to do this? If this is because you think memory is getting corrupted, you should only use the startup script and you should not try and do a graceful restart, as the corruption may prevent the shutdown needed for this.
Most people would only need something like logger reload.