I just added the %uniqueplayercount% variable to UltimateCore, which can be used in any message.
You could, for example, use the connectionmessages module and display a second message using the new line character (\n), where you display the unique player count.
Take in mind, because I just added it, that this feature is not yet in the latest release build.
I uploaded a compiled file for you here: https://www.mediafire.com/?2j4ki426o62m2mn
If you don’t like the other features, just disable all other modules 