We rejects posts that are not relevant to the network. So, the network will be niche specific but not all domain names will be. For example some "health" blog may receive posts about e-cigarettes and also weight loss stuff. It's not possible to make networks too specific, because then the networks would be too small.
You can also report bad posts for us to remove (we have a lot more control than other networks), we have an easy to access list of all posts sent to your blogs. You can check them from inside the member's dashboard, you don't have to look at your sites to see what is posted.