A lot of the drama of these programmes comes about because the celebs are not getting their N needs met, I think. In real life they easily attract the sort of adulation they crave, but stuck with a group of other famous Ns, they all become more and more desparate for attention. This means that a few members, often the older ones, get forced into non-N roles and usually end up cracking - for example Germaine Greer in the last series, who got cast as the mother figure by the rest of the group and abruptly left the series half way through! Well, that got her some attention anyway!
I agree, Dennis so far seems the most overtly N but of course the others may just be better at disguising it. My personal sense is that there are some absolute monsters in there. Unless someone like Rula has the nous to work out that Chantelle isn't really famous, I think she stands an excellent chance of getting away with it, since none of the others will be interested enough in her to notice, and she is already doing a great job feeding their N traits.