So long as one understands the Church’s position on ghosts and is firm in his faith, it does not appear to be a problem to watch such a show. However, if one sees it as inspiration to hunt down ghosts oneself, it would be problematic because the Church cautions against seeking out contact with spirits.
This is a bit different. Because the shows are fictional, one could consider them to be part of a “sub-creation” in which different “laws” exist (i.e., God could have created a world in which we were allowed to talk to spirits; if he did create such a world, what problems might we face in such a world?). Understood as a fictional construct in which hypothetical “What if?” questions are answered, there wouldn’t be a problem watching such shows. But if the shows might prove a danger to an individual’s faith or understanding of Catholic doctrine, then that person should abstain.