Gunbreakers do not use Garlean gunblades. Garleans have swords (and shields, lances, fists) that are also guns. Gunbreaker blades are straight from FFVIII and don’t have a barrel or bullets. The trigger activates an aether-charged cartridge loaded in the gun that does a magic effect or rumbles the blade. It’s also evident they’re different weapons entirely when you use your ranged attack to swing lightning at the enemy instead of shooting a bullet.
Considering Yoshi-P made fun of Garlean weapons in an interview and called them “bayonets”, I don’t think a job that uses them is likely. He said the only reason they exist is because he wasn’t involved with 1.0.
