Yes, you absolutely can dry brine a butt. The idea is that the salt on the surface coaxes moisture out of the meat, which then mixes with the salt and goes back into the meat. This then denatures some of the proteins creating a "sponge" that will more effectively hold onto the meat's natural juices. A lot of people prefer dry brining poultry because, unlike wet brining, it doesn't introduce any additional moisture, which some say can cause delicate meat like chicken to become soggy.
I think the best thing for you to do would be to try it and see if you like the results. I've never done it for a pork butt, but I have with chicken and turkey and I'm kind of on the fence whether I like wet or dry brining more. They both produce moister, more flavorful meat, but they're just different. The dry brine seems to give a more velvety texture and concentrated flavor, while the wet brine leads to just over the top moist and tender meat. Both are great and I honestly don't have a favorite.