Ranger handles ultra-violet images the same way it handles Bitonal, Grayscale, and Color images. The enumeration is defined in RangerConstants.h. If your header file doesn't have an enumeration for ultra-violet in RangerImageColorTypes then you should download the latest version from the Ranger SDK page at www.sbullet.com.
You will only be able to access ultra-violet images if an image of type "Ultraviolet" is defined in TransportInfo.ini.