Is it a raised ranch or a two story on a slab? How is the home laid out? Kitchen, living, bathrooms & bedrooms up and family room, laundry and utility down? Are the fit, finish and materials used consistent from one level to the other? Where does the main entry enter the house? What it is called is fairly immaterial, how does it function and what comparables are available? If there are truly fully and I mean fully exposed full height exterior walls all the way around the home, then both levels are generally included in the GLA calculation.
Depending on the market the real trick is going to be finding true comparables. If it is what I would consider a true raised ranch with the majority of the living/sleeping areas on the upper level and the family room, utility and laundry areas down, it is my experience that the overall value will be more similar to a traditional ranch with a finished basement and more specifically a walkout basement. Versus a more traditional two story home layout with kitchen, dining and living on the lower level and bedrooms up, regardless of whether it has a basement or not. Functionality is probably going to be one of the greatest areas of explanation regardless of what it is called and what comparables are used.