You don't have to rub your butt before smoking. In fact, while I haven't tried it yet, I will not rub the butt prior to cooking my next one.. rather add the rub to the pork once it's pulled along with whatever I plan on adding like some sauce. The high salt content of most rubs tends to pull moisture from meat, especially thin "cuts" like ribs if you apply the rub and refrigerate overnight.. you don't need dry"er" meat. The smoke will add complexity to the meat.. that taste we all seem to go bananas over. But, adding whatever you like as a sauce later will finish it off to your personal tastes. I'm sure my tastes are different from many here..
BTW, don't make a mountain out of a mole hill on this cook.. Butts are very forgiving.. you'll love the results on this first one.. and if you keep good notes.. you'll know what needs fine tuning.. then ask more questions