For the Hawaiian pulled pork: In a small bowl, mix the onion powder, salt, garlic powder and pepper. Rub the mixture on all sides of the pork. Put the pork in a slow cooker and cook on low for 8 hours.
Shred the pork with 2 forks, removing any large pieces of fat. Pour the broth into a fat separator or skim off the fat. In a bowl, whisk 2 cups of the skimmed broth with the crushed pineapple, hoisin, honey, soy sauce and vinegar. Put the pork back in the slow cooker and stir in the sauce. Cook on low for 1 hour.
For the slaw: Meanwhile, combine the cabbage, rice vinegar, sugar, celery seeds and some salt and pepper in a bowl and toss to coat. Let stand, tossing frequently, until the cabbage wilts, about 20 minutes.
Serve the pulled pork on Hawaiian buns topped with slaw.