When I was researching what would be best to use on my Beretta O/U, it was pointed out to me that the grease on the hinges performs 2 functions. 1 is to reduce friction on the bearing surfaces, which graphite would also perform. The second is to provide some cushioning effect between the surfaces to help prevent the two parts from hammering away at each other. I don't think a dry lube would do this.
It only takes a minute to wipe off the old grease at the end of a shooting day and apply some fresh stuff the next day out with a q-tip. Grease is cheap, as is a minute or so of my time if it extends the life of my (relatively) expensive shotgun.
Cheers,
Ken