Per a posting I read somewhere recently, they said that even if you are shooting raw, the camera histogram is based on the result you would get if you are shooting jpg.
Surely enough, while the histogram in Lightroom is not exactly what I see on the camera display, it is pretty close and definitly closer than when I was using the camera defaults.
WB changes the results more than any other setting. Research uni-WB and install it on your D300 for the most accurate histogram and determining whether or not you are attaining optimum exposures.
While the WB does have a huge effect on the histogram, one should not ignore the tone curve, either in the JPEG review or the rendering in ACR or Lightroom. With most subjects containing a balance of colors, the Green component of the camera RGB histogram will give the best estimate of ETTR exposure, since the green white balance multiplier is unity, while the red and blue multipliers are greater than unity. If the subject contains saturated red and blue (such as in pictures of some flowers), these channels may appear blown in the camera histogram while they are intact in the raw file because the red or blue multiplier results in overflow in those channels.
A hot camera tone curve may also cause the histogram to be too far to the right, and this effect can be more important than WB in some cases. For example, here are snapshots taken in my back yard with the Nikon D3 using the Standard Picture Control (normal contrast and saturation) rendering into Adobe RGB with daylight WB and UniWB. In the daylight WB shot, the exposure appears reasonably to the right. Since it was overcast, the picture is blueish. The UniWB histogram gives a better idea of the raw values for the red and blue channels, but this information does not aid in ETTR since the red and blue are to the left of green.
Daylight WB:
[attachment=18916:DaylightWB.jpg]
UniWB:
[attachment=18917:UniWB.jpg]
The ACR histogram with default settings appears reasonably exposed:
[attachment=18918:ACR_daylight.png]
However, if we look at the raw histogram with Rawnalize, the image is about one stop underexposed:
[attachment=18919:Rawnalize.png]
Both the camera and ACR are using a hot tone curve. In ACR an exposure offset of +0.5 stops is used, moving the histogram to the right by this amount. To get an ACR histogram better reflecting the raw data, one should set the tone curve to linear (all sliders on the main tab set to zero and the point curve set to linear) and look at the UniWB shot using -0.5 EV expose to cancel out the exposure offset that ACR uses. This histogram is still to the right of the Rawnalize histogram, since the ACR is using a gamma of 2.2.
[attachment=18920:ACR_as_shot.png]
For a better comparison, we need to convert the gamma to 1.0 and look at the histogram in Photoshop:
[attachment=18921:PS_linea...omposite.png]