I highly doubt she left him out on purpose. Joel Grey has said that due to his involvement with ANYTHING GOES he met with George C. Wolfe and disucced the production, saw that they had the same vision and let him take the lead. Obviously Joel Grey was still involved with the production, but much of the staging/concept has stayed the same from the Walter Kerr reading.
"Oh look at the time, three more intelligent plays just closed and THE ADDAMS FAMILY made another million dollars" -Jackie Hoffman, Broadway.com Audience Awards