For innervate or procs yeah it's doable. I would suggest going by the combat log event for those. You could do UNIT_AURA also but that will fire a lot more than the combat one. Events are being rewritten this weekend I'll try and remember to make an example of either to post.
For an event based on target type, you would want to trigger on PLAYER_TARGET_CHANGED and I suggest a delay of 0.25 or 0.5 since the event fires in pairs when you go from one target to another. The functions to check would probably be
http://www.wowwiki.com/API_UnitCreatureType