I've just completed a beginning Nosework class with my boy Luther. While I'm not sure whether it will help with dog reactivity it certainly helps to desensitize dogs to a large variety of objects and the other dog owners. We had a vizsla in our class that would not put his nose into a container in the beginning and by the end of the course he was happily rummaging in the bottom of toy boxes, shopping bags and coolers. Another dog was scared of umbrellas but learned to work around them searching for food. And Luther, who is timid around men, was able to walk past the male handlers without batting an eyelid. Added bonus: Nosework provided great mental exercise during the winter!