Well that's one way of looking at it, but who's to say the producers don't want the housemates questioning everything. They've already started building extra rooms after the show started, probably so that the housemates talk and question the things going on around them, and like in this scenario, the fact that this actress has maybe met some of the housemates before could only serve to increase the amounts of paranoia even more, which in turn can get the housemates doubting their own judgement or even sanity. I can accept there's a chance that the producers have been cheap and lazy by hiring a channel 4 employee, but I'd be more inclined to believe this sort of risk is something that they encourage. The shows about controversies, twists, secrets and mind games, so if you think about it, it's quite a good thing that the housemates could 'smell a rat' because they might counter the move from Big Brother with tactics of thier own, which will work out best for the viewers. Do we really want to see them all thinking they're talking to a real Australian? I'd have thought that would get a bit boring after the first day....
It's next weeks eviction I'm looking forward to - probably when Charley (or someone with a good reputation) goes back in after an interview - that's something the haters can all complain about too!