empty pockets
As a Junglie who posts every so often on PPRuNe, I can assure you that the RN has no specifically overt policy about posting or reading PPRuNe. While they would probably view it in the same vein as talking to the media if pushed (because you're expressing opinions in a public forum both without permission and without official sanction), most of us limit our comments and posts to encouragement of wannabes like yourself and, in the case of most RN PPRuNers, the occasional bit of crab-baiting!
The miltary forum tends to be self policing, so that on the few occasions that someone has posted information or discussion of a subject that shouldn't be aired in a public forum, the rest of the community tend to put them back in their box.
Having said that, you will find a lot of people willing to express opinions about policy etc that the heirarchy probably frown upon, but that's the beauty of an anonymous (mostly) forum!
Basically, you're unlikely to be binned for reading or using PPRuNe, but I wouldn't exactly make a point of advertising it!