Is it possible to hide certain tabs?

Yes this is possible and can be done by configuring permissions for specific users in app_settings.json. For example, if you would like only a national_admin user to see the people tab, you would set the permission as below;

"permissions": {
  "can_view_people_tab": [
      "national_admin"
    ]
}

This means anyone who is not a national_admin will not see the people tab.

There isn’t any documentation on this but there is an issue for that here.