The Zaross were a fictional race, created and used as a disguise by the Herazi, so they could be part of an intergalactic reality show, where the main race would invade a new planet every episode.
The Herazi created the Zaross, so that they would be taken more seriously by the various other planets and species of the galaxy. They used heavy makeup to hide their true appearance.
Under the makeup, the Zaross had the appearance of a bipedal warthog, with large tusks. Not yet aware of them being a fictional species, the Tenth Doctor thought that they looked very close to the Herazi, not realising that the Herazi were the Zaross. (AUDIO: Infamy of the Zaross)