It seems fine, though there is nothing preventing anyone from talking about the game in PMs since this is not Fight Club. *winks*
In the other game I'm in, I had a couple of different groups of people I was chatting with in PMs to work out a voting strategy while I was still alive to vote. It's tricky since only the rebels KNOW who the rebels are, so you can't (unless you're the historian) be sure who is or is not really safe to plot with.
And of course, you could wind up plotting with someone that isn't truthful... but that's what makes this fun, it is indeed a battle of wits to the death. *grins*