Mmmm… Maybe it is just a way to show that they are both more or less in the same bussiness:
Hook is a pirate -traveler of the seas, not exactly honest, blablabla- and Jefferson, the traveler between worlds, also amoral, blablabla. Hook has his ship -there is a special relationship between a capitain and his ship- Jefferson his hat -the passaport Jefferson asked Regina for remembered me to the letters of marque-.
Both know Rumplestiltskin, but while one wants to kill him, the other seems to be his friend (by the way, we don’t know if Jefferson ended in good terms with Rumplestiltskin or not. It is curious how he hates Regina, releases Belle… but have no relationship with mr. Gold, not even a single conversation during the whole series in modern times. Jefferson knows about mr. Gold, and I’m sure mr Gold knows about Jefferson.So… maybe there is the answer)
Besides, I always thought that the way Jefferson wears is similiar to a cyberpunk character, while Hook’s style is more “historical” -as much as it could be in a show like this-.
But you are right, they look quite similar.