Created the file here and now Software Update finds OS X Server as Update.
Open Terminal Window And Type the Following commands:
cd /System/Libray/CoreServices sudo cp SystemVersion.plist ServerVersion.plist sudo nano ServerVersion.plist
Next edit ServerVersion.plist and change the following which I guess is just a cosmetical change maybe.
<string>Mac OS X</string> to <string>Mac OS X Server</string>
I like to use nano. Easier to edit the file right from the terminal.
sudo nano ServerVersion.plist
Reboot and download Server Admin Tools Package.
I tested it on OS X 10.7 and when I ran Software Update the Server Package Update is listed.
Also I managed to install the 10.7.1 update from the DMG file. That didn't worked before.
Again sorry if I posted old news.