This posting is older than 6 months and can contain outdated information.
I just did have a look at the Jaman Player. A Behaviour for it is now 
available via Remote Buddy's Online Update.
A few things of note about the current version of the Jaman Player 
application (as of May 31st, 2009):
1) Jaman Player currently doesn't seem to properly support keyboard 
navigation / control. At least I didn't find any way to. I can 
fastforward and rewind with the cursor keys, I can press space to 
pause, but I can't find a way to restart playback or control volume 
via the keyboard.
2) Jaman Player does not seem to use any standard OS X GUI elements 
inside its window, but instead appears to draw all of its UI elements 
itself. Looking into Jaman Player's bundle it turns out it uses the 
cross-platform QT Framework for its user interface, so a lot of 
goodness available to truely native OS X applications that use native 
OS X controls and frameworks for its user interface is not available 
for controlling Jaman Player.
3) Due to 1)+2), the only working way I can see to control Jaman 
Player appears to be by the use of emulated Apple Remote presses - 
utilizing Jaman Player's built-in support for the Apple Remote.
4) Jaman Player does not seem to react to Apple Remote events once in 
full-screen mode. Therefore, remote control of Jaman Player in 
fullscreen mode - with or without Remote Buddy - does currently not 
seem to be a possibility.
That said, remote control of Jaman Player in window mode seems to work 
fine.
Best regards, 
Felix Schwarz