It's very possible that Deathfuse was king of the Ancient Robots, or is the Pirate King. The fact that he has a hook for a left hand suggests that he either lost a limb in a struggle/war of sorts, or had to challenge another robot in order to gain that title. That's hard to determine since there are only two robots that look fully humanoid in Skyward Sword. But if my speculations are correct in Hyrule-terms, then Scervo is, or rather was under the command of Deathfuse to begin with.I'm not so sure if Deathfuse really is suppose to be a pirate, I mean, look at him, he looks more like some royal robot.
Of course I think Scervo and Deathfuse have some kind of relation, they are most likely the same kind of robot. Perhaps Deathfuse was the king of some part of the surface a long time ago, and Scervo was a pirate who lived the that same country.