The basic cause for the difference between your JPEG image and the TIFF is that the JPEG is generated from the raw data by the camera's JPEG engine. The TIFF is generated from the same raw data by UFRaw's conversion algorithms. Both interpretations are equally valid results of the information in the raw image file, but they are different interpretations.

There's no single "correct" way to render a raw image file. It has to be demosaiced and developed to become a viewable image. Part of that process includes setting color temperature and white balance correction based upon the color of the light illuminating the scene. If you are using "Auto" color settings, each application will take its best guess at what color settings should be used. Each result that you see on your screen is one of nearly countless possible interpretations of the raw information collected by the sensor.

In the case of reproducing slides, if you are using a controlled light source that is consistent for every shot then you can create a custom color profile to use. The easiest way to do this would be to put some neutrally colored diffusing material in place of a slide and take a picture to set a "Custom White Balance" in your camera. Your camera's manual should explain how to set a "Custom White Balance". You'll probably also find it better to use the Neutral Picture Control instead of Standard. If you then open the raw files of your slide photos in Nikon's ViewNX the CWB should be applied to the raw information. (If the default behavior of ViewNX is to use another method for color development, you can always change it to apply the CWB.) You can probably also apply the same settings to many images using a "batch" function from within ViewNX but I'm a Canon shooter and can't help you with exactly how to do that. This will allow you to consistently duplicate what each slide looks like, but it will not correct for any imperfections in the color of the individual slides themselves.

If you are interested in optimizing each slide, please see Why can software correct white balance more accurately for RAW files than it can with JPEGs? There are several links at the end of the accepted answer to that question that you may also find helpful.

In the case of raw vs. TIFF. vs JPEG, both TIFF and JPEG already have the color more or less "baked in", though there is a bit more latitude to alter the color of a 16-bit TIFF than to alter the color of an 8-bit JPEG or 8-bit TIFF. Neither allows anything near the amount of color and exposure correction that working with a raw file does. The accepted answer to the question linked directly above goes into much greater detail about this.