It just so happens that I have been researching this exact point for the next update to the
Barbarian Paper.
Your observation, Tavis, is absolutely correct, the Barbarian leader does get all his unit stats from the diplomat slot in the rules.txt file. Therefore, you can transform the barbarian leader into an attacking by changing it's role, a flying unit by changing it's domain, and so on ...
This, of course, opens another window of opportunity for creative scenario designers.