Technically you can DNW x/z fic but you can't stop a writer from writing the two characters while skirting around an actual ship but having them act in shippy ways and still labeling it gen. I've been on the receiving end of that myself. Some are more transparent than others.

Also, shipfic does not equal porn. Not sure if that's what you're saying with the last sentence or not, but if so, not the same.