While I "main" Monk and Warrior, and Endemerrin is most proficient in the two, his youth saw him tailored towards the use of Magitek in combat. It's more of a hidden talent, as he doesn't carry around a full arsenal, but he's fully capable of wielding a Gunblade and using a variety of Magitek in combination with it. Even outside of that, he has various tools he carries with him that he'll use from time to time, such as the Magitek grappling hooks and Flashbangs we've seen used in-game. He is a Magitek Engineer at his core, and I'd say that would be his unique "job".
And given his wealth of experience working with and creating Magitek, he picked up many of the traits necessary to be an Armorer.
And given his wealth of experience working with and creating Magitek, he picked up many of the traits necessary to be an Armorer.