Unless rogue armies are at war with you, they tend to avoid targeting armies. See each individual Rogue Armies faction page for details on which units they can recruit. For instance, Vashnaar's Conquest can recruit units from both Dark Elves and Chaos Warriors rosters, while Pirates of the Far Sea can recruit units from The Empire and Bretonnia.
This often includes units from several different races. The various different Rogue Armies factions have different unit rosters.
