I believe they are inexorably linked. At least in me they are-- Alanon, over the course of 13 years, has helped me to manage, mitigate, and stifle most of my passive-aggressive behaviors, and be aware of my codependency issues which are deep-seated and profound. Now I'm less codependent and directly aggressive which is a step in the right direction-- no more passive aggression for me! Now all I have to do is figure out a way to not be so attracted to profoundly f***ed up people and their "ism's. "
And, very respectfully and IMHO, playing diplomat is codependent and passive aggressive. It's the go-to for people like me, and very much appeals to my super hero complex. Recovery, at least for me, means not playing the diplomat. The relationships between other people are none of my business-- they are responsible, fully and completely, for the dynamic of their relationships. I'm out! My relationships are my business, and not anybody else's.
That doesn't mean I don't exercise diplomacy when communicating on my own behalf, but that it's not my job to be doing it for anybody else-- especially an alcoholic/addict.