If you shoot in RAW, the in-camera noise reduction probably does not take effect, and if it did, it is really reducing the value of RAW on your camera. When you shoot RAW, you really just want the original output from the sensor with as few modifications applied as possible...none at best. You have far more control over noise during post processing, and far better algorithms at your fingertips to combat that noise with the more powerful software you can run on your computer.
I would recommend you keep your RAW images as bare-bones and neutral as possible, giving you maximum capability in post processing. Noise reduction, highlight tone curves, and other such features should generally be disabled when shooting RAW. Additionally, its normally (but not always, sometimes you may wish to choose alternatives) best to use AWB and the standard or neutral tone curve/picture setting of your camera to produce as "original" an output image as you can.
Dark frames are a slightly different matter than your average noise reduction. They can be useful when you are doing very long exposures, such as during astrophotography. You should enable Long-Exposure NR/Dark Frames on an as-needed basis when the shoot actually calls for it.