Their wiki page has that listed right next to a requirement that the General be a Hero, so I think it may actually be a class requirement.
Is that an IR gray area? It makes plenty of sense ICly but let's say you're a cavalier, you get elected ruler, then you want to change classes for a while and you can't?
Well, some theocracies only let Priests be the Ruler so I don't see how that would be much different.
