>How are you interacting with opponents in rowing? Can you hit them over the head with an oar?

Words can hurt more then an oar. :) Either way you'd have to hit them really hard for them to care (they train insanely hard).

>By politics I mean that you can cooperate with a part of your opponents to side line some of the other opponents.

I feel i can safely say that that doesn't happen in rowing. At least for the team i know i am sure that they wouldn't "take a dive" (or even think about it; same for their trainer).