My version of the Nik plug-ins are also the Lightroom/Aperture licensed versions. If yous are the latest or second latest versions, they will also run as a standalone program. If you look in the program folders for those plug-ins, there will be an executable. Most of the Nik plug-ins (HDR Efex being the main exception) do not have the ability to select a file to open, you need to use CNX, PM or your system file manager to "open with".
Photo Mechanic is very easy to use, and its not a cataloging program, so you would not create a separate database. You can get a free trail from the Camera Bits web site.Someday they will issue the long-awaited catalog module for Photo Mechanic, but you won't lose anything as it is intended as an add-on to the regular PM.