".zoo" files are not like ".ztd" files. They are in a format that only Zoo Tycoon understands. Inside Zoo Admin's downloads database, there is a section for "Maps and Workbenches", including "blank" maps, although they are not totally blank because they have zoo walls. However, the downloads database is still being updated. So that section has not been updated yet. These maps were created using the Map Editor, which is available in the Utilities section of the downloads database.
As Yellowrose said, these maps are actually saved games. So you would have to load them in Zoo Tycoon like you would load any other saved game.