No, all national WWOOF organizations are separate entities and you need to join each one separately.
Hosts located in the 80+ countries without a national organization are listed on the WWOOF Independents website, which is directly managed by the Federation of WWOOF Organizations (FoWO). WWOOF Independents’ members can contact hosts in any of those countries.
Several countries are working together so that in the near future, your account and profile information will transfer between most WWOOF organizations.
Please visit wwoof.net for information on other WWOOF organizations around the world.