1. Most Single Units.
2. You cannot, and I don't think there are otherways to get henchmen.
3. Yes, XP split exists among heroes and not henchmen.
The henchman defining feature is not that they do not divide battle XP, they have other features about them and there is a tag that can set for any hero just the same. It is also not like that Mausolos cannot be left alone or moved to another army. He doesn't have to follow you around.
Thanks for the answers.
I understand that heroes can be split. My point was that the story line of Mausolos in particular makes the xp split especially glaring. His whole story line is that he will act as guard for the hero completing the quest (in this case my Sovereign) until the end of time. Except... that if you actually do that you're penalized.
I'm not complaining about the xp split system, per se, more pointing out that in Mausolos' case it shouldn't apply.