Basically its a global chat channel. All the rules (or lack of) that apply to every other channel in the game apply to NN. You're free to discuss whatever you want even if its not related to helping novices but if you say something too risque then someone may find it offensive and report you, just like any other chat. If someone is saying something offensive then report them and let the GMs look into it.

Personally I don't find those topics appropriate for the NN but depending on HOW they talk about it I probably wouldn't report them. I may find it a distasteful subject but that doesn't make it reportable. if you found it offensive then please report it. I know GMs don't punish people for bad reporting as long as you aren't going crazy with it.