abbadon: Honestly I will not prejudice myself against the game because we never know. Personally it looks epic and I can not wait.
I don't think they will ruin the story, but let us not speculate let us be patient and wait.
As for recruiting sentinels it will be a cool addition to the game.
IS it Canon? does it fit in with Halo? Does it make any sense at all? no no and no.