All right, I'll chime in.
Playing to the edge of the refs wits with regards to offside and the breakdown are part of the professional game. All sides do it.
To deliberately impede the endeavor of the other side, by repeatedly infringing against the rules of the game is still probably within the referees discretion to enforce.
However, if players or an entire team keep infringing in a manor that is purposeful to halt the momentum of the other-side in a manor that is against the fabric of the game, despite being penalised - I think you are then moving into the realms of cynical play. Or rather, if your instincts are to stop the other team playing rather than playing yourself, your actions are in fact cynical to the foundations of the game.
When Greg Chappell instructed Trevor Chappell to bowl the infamous underarm delivery at the MCG in 1981, he was stopping the contest by not allowing the other team the ability to 'play'. While technically legal at the time, his motives and actions for the delivery and outcome of the contest were cynical.
I believe with this logic applied the same conclusions can be drawn from how the Brumbies played last week.
But at the end of the day, we are merely talking about ethics, which is for all intents and purposes philosophy and semantics. It is the referees job to enforce the 'ethics and rules' of the game, and he attempted to do that, albeit with a distinct flavour of inexperience and I'm sure he would referee the match differently in hindsight.
The Brumbies aren't a dirty outfit, they just did what was necessary to keep themselves in the contest, which is the hallmark of a champion side. Jake White is one of the most street smart coaches in world rugby, and it is the very reason that he is a champion that drags success with him wherever he goes.
While it was not entirely ethical, the overlap between professional sport and ethics is rightfully or wrongfully non-existent.