Are you new to Nuke 6.5??
You didn't had to add smartDark and the Default theme for the forum is always the same as for Nuke so if your smartdarks forum folder is placed in themes/YOUR-THEMES/ and that theme is your sites default smartDark will be your default on the forums too.
So to fix it go into your database go into your table nuke_bbthemes and delete there smartDark.
Then go into nuke_bbconfig and look for default style and change it to 1
Then go into your site and go to nukesadmin and change the default theme to the theme you want.
Then go to the forums an you should see smartdark there and in your nuke will YOUR-THEME be used.
Sorry for the long explenation in difficult english (for me
) so if you don't understand it please mikem or the others save him from my terrible english
.