Reese has warmth and he understands the distinction between Doing The Right Thing and Following The Rules. I suspect he also has a wicked sense of humor, all the more effective for being camouflaged by the gruffness. All of those traits would stand him in good stead when he's dealing with Mozzie: he'd see past Mozzie's eccentricities and, um, moral ambiguity to recognize his good heart and vulnerability.