An iMac Intel Core 2 Duo:
- Mac OS X 10.6.6;
- ARD Client 3.4-current;
- WAN-side TCP & UDP 22, 3283 and 5900 forwarded to the iMac.
- In desperation, I DMZed the administration target.
Before DMZing my administration target (i.e., with only 22, 3283 and 5900 forwarded), the iMac is listed as "Offline" on the Remote Desktop administration screen. However, I can ssh into it from Terminal.app successfully and I can control the screen — I simply can't do any 'special' tasks (copy, install, report, restart, sleep, etc): I essentially can't do anything other than viewing/controlling (and locking) the screen.
Once the host was DMZed, my administration window lists the node as "Screen Sharing Only".