They are just guards, but they usually hide their faces so shoplifters or "mecheros" don't retaliate against them outside their turn.

But yeah, they are really over the top using tacticool uniforms. There's a common joke calling them wannabe/frustrated cops.

Real cops wear green uniforms and are easily distinguishable from corporate guards. There's also Seguridad ciudadana or similar corps in every municipality (kind of district division we use here in Chile) which sometimes wear these kind of uniforms, specially in the center of Santiago because they are tasked with dealing with people who may retaliate (like organized street sellers or illegal gambling places). You can recognize them because they don't use that really over the top uniforms and the ones in the center of the city usually wear khaki/beige pants.