Yes, deer have a very keen sense of smell, the best thing that you can do is watch the wind direction. In my experience, most of these scent killer products are highly over rated, and definatly over priced!
Good hygiene, and plain old baking soda, works great! As far as guns stinking, yeah if the deer is within 3 feet of it, they can probably smell it, but gun odors do not spread like other human, and chemical odors do!