This confuses me. How come Yue's dad never opposed Yue fratinizing with Sokka is she is engaged? How come no one makes as much fuss about Sokka's interfering with custom and tradition as they did with Katara? Did Chief Arnook know Hahn didn't love Yue? Was he ever really serious about the marriage since he'd seen the future and knew Yue was a future spirit?
Sokka & Yue didn't really break any rules, & what they did do happened mostly out of view. Their attraction was a social faux pas, but Arnook saw it more as an opportunity to have someone who would protect Yue. He could tell Sokka obviously cared about her more than Hahn did. Hence him telling Sokka that he took him off the mission because he wanted him to protect his daughter.