A prisoner's dilemma situation requires good outcome if everyone colludes, and a terrible outcome for all if even a single prisoner defects. I don't see a terrible outcome for all if one hotel greatly reduces their price.
No, that would be collusion. They would be running a cartel and that would be illegal.
Worse, your speculation that Buffet is doing this to get hotels 'to break rank' is absurd. Metropolitan Omaha has ~10,000 hotel rooms (source - http://www.visitomaha.com/meetings/faqs/#.U0R2_61dUnI) compared to the 30,000 people who plan to visit _just_ for the shareholder's meeting. There is far more demand than there is supply of rooms, this is simply a rational response to that.
Nope, this is exactly what would be predicted by Econ 101: Microeconomics. The demand curve during the shareholders' retreat is shifted up/out relative to a normal one during other weekends, leading to higher prices even given no change to the supply curve.
This is really just competition, with the possibility of collusion, which is very much Econ 101.
The situation is like a prisoners dilemma for hotels. If they all raise prices and none of them break rank in price, then they all make more money. BTW, just by pointing out the option of Airbnb, Buffet makes it more likely for a given hotel to break rank in a collective price bump.
Another way for Buffet to break gouging might be to publicly announce the price spikes as something driving consideration of future alternates for his meeting. But his past behavior makes that unlikely given that he would likely have to shift to areas with larger travel markets so as not to be a large percentage of the existing travel capacity of the locale.