If you blanch then dehydrate veggies, then cook for one hour on the trail, you will destroy just as many nutrients as you would simmering for one hour at home.Better to do the simmering at home IMO so as not to waste an hour's worth of fuel (and the time) cooking it at camp. As stated earlier, make sure you chop the veggies to a uniform small size or rehydration will be varied (incomplete in big pieces, over cooked with small pieces. Should be no need to whiz in a blender if small pieces are used - just crumble in the fingers. Personally, I like "cream of" soups, and usually blend as a final step in cooking, but I can understand that some would prefer the soup to be chunky, but the chunks must be uniform and small. Re nutrients, when hiking, I always expect that my diet will be short of some essentials, so I take a USP daily multi vitamin pill to compensate just in case.
Re veggie soups in general: I like them very much, but when hiking, a veg soup is very low in carbs and protiens, so would not be anywhere near a complete meal. An exception, of course, would be if the soup has a large content of legumes, in which case it would really be a bean soup, not a vegetable soup. I f you are hiking any distance, you need carbs and proteins in quite large quantities as part of your meal.