As Earl said 28s stopping at Hermosa or not depends on a few things. You stated that when you rode during foamfest they always stopped. That seems to hold the answer in your statement. If it's a photo charter that is going to make a few photo runby's before the next water stop, then of course they will stop for water.
Under normal circumstances the 28s just go right passed Hermosa.
Another reason could be not enough water in the tank when it left Durango. Maybe it didn't get filled or the engine was brought out to sub for another loco and there was no time fill the tank.