Yes there are certain topics that the hubpages team will raise red flags on. And as you already have mentioned-topics that contain adult content etc... are usually a no-no. However you can find out more about this in the either the hubpages learning section on the site, or under the FAQ's section.In addition there are built-in filters when you are writing your hub, that will give you a warning letting you know exactly what may need to be changed within the hub, before it is finally published for everyone to read. Hope this bit of info. helped answer your question.