The profile that applies to events sent by Remote Buddy's Plex Behaviour should be the Apple Remote, not the Harmony Remote. That aside, Remote Buddy always sends the same UDP data for each button press - and it's completely up to Plex to interpret that input and map it to an action using the respective xml file you mentioned.

To use Plex' Harmony mode (and profile), you'll have to set up Plex and your Harmony accordingly and configure Remote Buddy to simple pass through all Apple Remote events. A few years ago, I've put together a step by step guide for this, which you can find here:

http://www.iospirit.com/blog/article/131/Remote-Buddy-and-Boxee-Plex-and-XBMC/

Best regards, 
Felix Schwarz