It is an interesting point. If RMR could buy up 5% of the stock for itself, that could be enough to defeat the vote, since 2/3rds positive for a new board is necessary, and 5% base positive for RMR makes Corvex get 72% on the remaining vote with the other shareholders. But 5% is $150m, a large sum of money, and to put that into the stock would move it up, say to $28.
Then, oddly, RMR would have different possible risks and benefits. If a positive vote to eject RMR, they would make money on the stock purchased, but lose the contract with CWH. If a negative vote, they would keep the contract, but lose big on the stock, since the price would crater to $18 or so.
I doubt RMR will attempt to buy much themselves. Too much money, and they do not want to actually own the stock. And I doubt they can line up commitments to vote for RMR: what would the consideration for that be to a shareholder?
It is quite possible that arbitrageurs will be buying or selling short this stock based on what outcome they expect. Or they might not much come in, being too uncertain of the odds, and a notion of where the price would settle with each outcome.