I don't brine pork, just dry rub and rest like you say. I've never tried it to be honest (that I recall) but I get results I'm happy with, without the extra prep work. I do wet brine chicken every time, then use a light-flavor rub after rinsing and drying it. I just don't trust chicken.
Fat cap: with my setup resting on a pan+grate in the smoker, I'm pretty protected from the heat by the tray and grate to begin with. However I still always put fat cap down because:
1) I'm not sure if rub really does much through even a light or trimmed fat cap anyway (I still put a little on that side)
2) I want to be sure the bare meat is as exposed as possible to the airflow of smoke
3) when doing a pork butt, the bottom (fat) sometimes sticks a little bit to my butcher paper -- if it's mostly fat I don't care and it's maybe 5% easier to yank out the meat and pitch out the fat layer
4) I nearly always inject marinade to be 100% certain I have all the liquid I need to end up with a juicy result in the end (plus some savory flavor)
5) there's so much marbling in a typical pork butt in particular, worrying about how the fat cap interacts seems redundant
I probably agree with Meathead that it's a quibble that largely doesn't matter at all. You can get a great result putting the meat in any orientation. It's several other variables that have much greater impact that determine success.