I'm not sure if TN is actually a Skyteam partner however they are an airline partner with NW. If you are a NW/DL Worldperks member you can redeem miles on TN but I don't believe you can earn miles. From the NW site:
Redeeming Miles
WorldPerks members may redeem WorldPerks miles on select Air Tahiti Nui routes: Los Angeles-Papeete, New York (JFK)-Papeete, Tokyo-Papeete, Osaka-Papeete, Papeete-Sydney, Los Angeles-Auckland, Tokyo-Auckland and Osaka-Auckland.
Destinations
Located on the French Polynesian island of Tahiti, Air Tahiti Nui serves 7 cities to/from its hub in Papeete.
Web site: www.airtahitinui.com
Award Blackout Dates on Air Tahiti Nui Flights: None
As a side note, it looks like Wikipedia may have pulled some of the information from the NW website since the following are all partner airlines with NW:
* Air Tahiti Nui
* Alaska Airlines
* China Airlines
* China Eastern Airlines
* Garuda Indonesia
* Jet Airways
* Kingfisher Airlines
* Malaysia Airlines
Perhaps the NW/DL merger is what's driving some of the speculation that one or more of the above airlines will become a member of Skyteam.