How do you use the mercenary portals in dungeon keeper 2

You just get your Imps to claim them like regular Portals and the different rooms in your dungeon attracts the Heroes version of the creature it normally spawns

Example:

Normal Portal + 5x5 Hatchery + Workshop = Bile Demon

Mercenary Portal + 5x5 Hatchery + Workshop = Giant



Normal Portal + (Minimum) 3x3 Library = Warlock

Mercenary Portal + (Minimum) 3x3 Library = Wizard