Sprinkle salt over entire pork shoulder and place in a slow-cooker with crushed garlic, cumin seeds and 1/4 cup vinegar. Cover and cook on low heat for 7 hours or high heat for 5 hours. Pork should shred easily and be very tender.
Meanwhile, make slaw by whisking together remaining 1/4 cup vinegar, sugar and celery seed; toss with onions. Let sit up to 3 hours. Stir in cilantro just before serving.
Remove pork from juices and cool slightly, then shred and cut into small pieces. Strain juices and pour off fat. Mix 1 cup of the juices with barbeque sauce and hot sauce to serve with pork; discard remaining juices.
Serve pork on brioche buns piled with onion slaw and drizzled with sauce. Pork can be made a day in advance.