Killing a player from the enemy team usually awards experience, and this is visible in a special menu, here:

In attached video, I was a FIA Renegade and killed a player from the enemy team (USSR), but either I didn't receive any experience or it wasn't displayed in the interface.
Steps to reproduce:
1. Become a FIA Renegade
2. Kill a USSR player and a separate US player to rule out any faction influence.
3. Check that experience isn't awarded or displayed in the UI.