I think it's better to add some XP changing events in unitlessEvents:
UPDATE_EXHAUSTION
UPDATE_FACTION
CHAT_MSG_COMBAT_FACTION_CHANGE
UNIT_PET_EXPERIENCE (maybe not needed but I left it)

The unitless event list is exposed, so layouts that need to add extras can. I see no reason why these should be added to the default list when they aren't used by oUF.