He never said to Dreamz that he had to TRY his hardest to win the challenge.
Dreamz can just sleepwalk through and still maintain his word. Yes, Dreamz cannot win immunity for himself (without breaking his word), but it seems like an expensive price for the opportunity to vote out one individual, especially an individual that seems like he wouldn't be a bad choice to have against you in the final 2.
The 5 person vote should be damn interesting (Also , why are they going to the finale with 5? is there going to be a "twist", or are they really going to have three tribal councils?)
fo the 5 person vote, the daggers seem like they are goig to be damn sharp. Yao and Earl are now a semi-isolated block onto themselves. Dreamz and Cassandra likewise. Boo is a semi- free agent (but he sided wth Dreamz/Cas last time, so call him leaning that way).
Buuuut... Yao and Earl have ONE immunity idol that is currently unrevealed (but you gotta figure the others suspect they have it, having been to the island the last two times), the playing of that is going to be a huge game of liars dice
OR they'll likely be able to swing one of the the others (boo?) to avoid the POSSIBILITY of having to go against the idol.
this seems like its gonna be a scheme-fest... hope they don't disapoint
(I think Cas is history, but she has shown herself to be a decent schemer herself)