people, please pay attention to the manga... That technique, is NOT a summoning jutsu. IT is a mokuton jutsu, made while hashi is in an unknown SAGE MODE. There is no such think as a fire sage mokuton sage, water sage,etc, unless kishi changes his mind.
This is likely the thrid sage mode that is obtained from training at the damp bone forest, which is the thrid legendary place.
So like naruto uses rasengan, and senpu rasengan(sage art rasengan) hashi has mokuton, and senpu mokuton(sage art: wood style)
This should be easy to grasp.
So if hashi did senpu mokuton wooddragon, his wood dragon would be bigger, and stronger.
The sage mode only increases the power of the user, and of his techniques, as well as upping his senseing skills, and durability.