What SPECIAL stats are useful in crafting rooms?
Solution 1:
All of them (but not at the same time)
Each crafted item has a specific SPECIAL stat associated with it. Putting dwellers high in that stat into the room reduces the time to craft that item. Bonuses from outfits do count.
For crafted outfits, the stat is the same as the highest stat of the finished item. For weapons it's less easy to predict, but you can see the stat in the crafting list.