I often find myself needing to remotely restart the Apple Remote Desktop service on various servers. There's a command line utility named "kickstart" that allows you to install, uninstall, activate, configure, and restart various components of the ARD service without restarting the server.
The kickstart utility is located here:
The command I am most interested in is:
$ sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -restart -agent
This command allows you to restart the ARD Agent and once again RDP into the server.