A DO without a point cost cannot be drafted into a player's army, but can appear in a game due to a map, scenario, or special power.
DOs with point costs and uniqueness ( Common, Uncommon, Unique, or Event ) may be drafted into Armies as Heroes can, following the same drafting restrictions as Heroes of the same uniqueness unless the scenario rules for a game mention DOs specifically.
Drafted DOs have their associated sculpt placed on the battlefield following the same scenario rules for that game as Heroes of their uniqueness unless the scenario rules for a game mention DOs specifically. When placing DOs you have drafted, you may also place any figures in your army on the card of that DO as occupants, assuming they can legally be placed in that DO.
A DO drafted by a player is included in a player's army, but is not automatically considered under their control and does not count towards the standard victory condition (if you only have DOs left, you will lose the game).