I noticed that in CS6 x64, the Nik plugins install manager picks up CS6 x32 and CS6 x64, and installs them both. However, when you pull up an image in CS6 x64 with the Nik plugins installed the image will not display on the workspace. It displays in the Navigator and the plugins themselves, but not the workspace.
I realize Nik is probably not certifying their products with CS6 yet, but all my other plugins worked so I thought I'd try. I'm currently reviewing the Nik suite of programs for Nik and have sent in a query.. but if anyone else notices they're not getting an image displayed on the workspace and they have a Nik plugin installed.. this post might save you a few minutes of trouble shooting. I'll post Nik's response.