If you don't see an icon on top panel it doesn't mean that the Remote Desktop service is not running. By default, you might see the icon when somebody is connected to your computer but you can change the default behavior by going to System->Preferences->Remote Desktop and checking "Always display an icon".
Coming to your second question.. After you SSH to the machine, try the command
to enable Remote Desktop. No need to add "sudo" before the command.
gconftool-2 -s -t bool /desktop/gnome/remote_access/enabled true
I hope this helps.