G'day ampclamp,
I'd heard the exact opposite - that if you don't do the survey you're engaged. Kind of like if you're too apathetic to do the survey you mustn't be all that pissed off. Happy to be corrected. I'd also heard that senior execs bonuses were linked to improving engagement, so I guess they'll be spinning that any way they can so they can put their hands in the till (again).
IMHO, what needs to happen is one of the unions needs to run exactly the same survey and collect exactly the same data, so that when the company comes out with its bullsh!t interpretation of the results we can call their bluff.