As long as it is perfectly nuetral, I do not see why not. If it is slightly warm or cool at all, it will cast your photographs in one direction or the other. You can test by taking a reading, and then taking a photograph of a colour chart and seeing how close it gets to the intended values. It would surprise me if it is, but you never know. Cards are cheap, and if you shoot TIFF or JPEG it would be valuable. If you just shoot NEF files, there is really no reason to spend extra on a perfectly printed grey card since the camera just assigns white balance as a formality.