Imma stop you right there. Addams Family is great, but it's not scary. It has spooky imagery, but only as a set up for the comedy that is a normal functional and loving family that simply does things differently than the squeaky clean picture of suberbia in the 50s/60s.
One could argue that the song is being sung by outsiders of the family. Since the song uses "They're", the narrative of the song means an outside entity singing the song is not part of the family. This furthers the theme of the show being about outsiders in suberbia and that the family is not a threat.
Sheesh, use your imagination. Yes, it was a comedy. But think much fun would it be to be laughing and all of the sudden get the poop scared out of you. How many horror movies are so campy scary they're laugh out loud? Zombieland, Behind The Mask....etc.
I'm not going to design a haunted house/maze here (that's a different thread), but I can think of many ties where people let their guard down laughing only to have the bejeezus scared out of them.
But it was an example of co-promotions that could benefit both parties...not a TV series/movie review.