1. 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 over low heat for 7 hr or high heat for 5 hr. Pork should shred easily and be very tender.
2. Meanwhile, make slaw by whisking together remaining 1/4 cup vinegar, sugar, celery seed; toss with onions. Let sit up to 3 hr. Stir in cilantro just before serving.
3. Remove pork from juices and let cool slightly, then shred and cut into small pieces. Strain juices and pour off fat. Mix 1 cup of the juices with barbecue sauce and hot sauce to serve with pork; discard remaining juices.
4. Serve pork on brioche buns pilled with onion slaw and drizzled with sauce. Pork can be made a day in advance.