Making the port NVA will help keep other sims when getting stuck there, and they should not be able to move into a lot designated NVA either. Your sims can move in; but if you keep the NVA designation, I believe visitors to your home will route fail.
There are three ports that are notorious for causing stuck sims due to routing problems. Those are the ones I designate NVA. You can always help the sim you are playing to navigate better. (I use NRaas Go Here mod.) You just don't always notice when other sims have problems there. Overwatch, of course, helps a lot.