Pokémon can only have 1 ablity at a time, so a Zangoose will either have Immunity or Toxic Boost. If it has the ability Immunity, the Toxic Orb won't do anything, but if it has the ability Toxic Boost, it gets the attack buff after getting poisoned by the Toxic Orb.
To resume, the effect that a Toxic Orb has on a Zangoose depends of its ability.
Source: Experience
Hope I helped!