Can’t prove it. According to Wikipedia (I know), Tomlin is from Michigan and Travolta is from New Jersey. There is no mention of a relationship on IMDB, either.
It seems to be a common thought, but there doesn’t seem to be any evidence that they are related.
I was thinking about this some more. And i’m pretty sure I remember reading in reader’s digest about john travolta a few years ago and the article there said they were related some how.