[Dead By Shaun]

Originally Posted by Ernest Rister

"Here, by way of making it up to you, a little bit of a hint. The music of Azog has caused something of a stir this weekend. Why does his last scene in the film include music we've previously associated with Mordor? I can't fully answer that question, but I can lead you a bit: Azog's primary theme is a descending pair of thirds (G-Eb-F-D) with a chromatic snap at the end (Eb-D-Db). Musically, Azog has a connection to Mordor's musical world from his first appearance on. His final scene is very much in line with this approach. Why this consistent connection? We shall see ..."

He doesn't answer the question, only implies it will be explained in the next two films, which suggests Azog is working for Sauron.

Exactly, because he's been explicitly told by the studio not to reveal plot details for the next two films, so he can only merely hint at it instead. The bottom line is the reason that particular musical cue was used was to

[Show spoiler]establish a connection between Azog and Sauron, which will be further explored in the next two films.