S-Bear = Kuma's DF, its obvious that when Kuma was with Vegapunk, he managed to work on it.
S-Shark = It was suppose to be a non-DF user like Jinbe, but somehow Vegapunk copied Senor Pink's ability, which is the perfect DF for Jinbe to swim wherever he wants, and put it into S-Shark. As for how Vegapunk worked on Senor Pink's ability, is obviously because of Doflamingo being a former Shichibukai, they probably asked from Doflamingo (when he was still a Shichibukai) to work on Senor Pink's ability.
We also see that Vegapunk somehow copied Jinbe's fishman karate as well, not only put a DF ability.
S-Hawk = ???
Obviously, as every Seraphim, it has cyborg lasers and Lunarian dna. But what else?
We know it can literally reshape an island via a gigantic slash, and easily cut a huge mountain with its sword. S-Hawk definitely has one of the best sword feat in the series already.
Did Vegapunk just copied Mihawk's sword skills like he copied Jinbe's fishman karate? Its highly possible.
Could it be more?
When Daz Bones was in Impel Down, perhaps Vegapunk had the opportunity to copy Daz Bones's ability into S-Hawk's body or into S-Hawk's sword.
Or, when Inazuma was a prisoner in Impel Down, they had the chance to work on Inazuma's cutting ability, and put into either S-Hawk's body or his sword.
If there is no DF power on S-Hawk, then it would be a much downgraded version of Mihawk compared S-Shark to Jinbe, I am guessing either they put a very usable DF ability, or somehow Vegapunk managed to copy Mihawk's Haki (similar to Oden's Haki being inside of Enma) and put into S-Hawk's sword.