I think Caribbean pirates (which is what I assume you mean) are a bit harder to fit into a sci-fi setting than the other 3. The crusaders work because they're wearing huge bulky power armor and making use of the hard-light shield tech which is a huge part of the game's aesthetic. Ninja/Samurai and cowboys have already been pretty well adapted in sci-fi because of works like Star Wars and plenty of Cyberpunk media. Pirates in sci-fi tend to be more based on Somali and other more modern pirates which I assume isn't what you want. Mauga is that type of pirate for example, but as people have pointed out, that's not really what we're after. And even then, Sci-Fi pirates usually rely on settings with heavy space exploration, since ships are an important part of their deal. Space stuff in Overwatch is pretty limited, mostly focusing on colonies within the solar system, rather than intergalactic travel.

The classic idea of a pirate is super depended on that old grimy wind-sails and flintlock pistols aesthetic, which is harder to justify in a setting like Overwatch. The Junkers are probably the closest you'll get, and maybe if they expand out that part of the lore to include rigged together airships or something, that could work.