In a game on a small map, I managed to recruit three units. And since the hero easily gains the "Harbinger of Death" skill, the unit is immediately converted into undead.
On a large map, the hero will be much more useful.
Everything about Diplomacy is described in the game mechanics.
P.S. Thanks for removing those garish numbers in combat.)
P.P.S. I don't know if this is a bug, but after 15 levels, playing as Hiormel, I only received a bonus to knowledge once when choosing education; the rest of the time, only magic skills increased.