All heroes in this mod has at least one special unit that they can always recruit, regardless of their current faction. For example, Huang Gai can recruit the special unit "Elite Fire Fiend" no matter which lord he currently serves.

However, due to the faulty coding of the game, these special units may fail to show up in the available unit recruitment panel. This is most common to heroes spawned via events or scripts like Zhuge Liang

To fix this, simply save and reload. You should be able to recruit the heroes' special units afterward. Keep in mind that most special units requires heroes to be level 5 or higher