There are plenty of ways to keep pulled pork warm. Not all of them are Health Dept approved if you are apt to get inspected. Crock pots are not legal--Rival home roasters are not legal. Chafing trays are legal if they are marked NSF. Steam tables are legal. Propane fired steam tables sometimes fail fire dept inspection if you are serving out of a tent.
I have seen broth, apple juice, water mixed with liquid smoke or other things added to pulled pork to keep it moist.