It's not going to hurt Trump, because it's not Trump who's saying it or even somebody currently with the campaign, just some wannabe hanger-on.
I can't think this is going to motivate people to "discover" anything about Hubbell and Clinton because everybody who cares about it has already heard the rumor a quarter century ago.
It's a pretty stupid rumor. You've only got to google "Virginia Clinton Kelley" to get an idea of where Chelsea's looks came from. And anybody who believes both the Hubbell-Chelsea story and the Hillary lesbian rumors probably isn't playing with a full deck.
I agree it won’t hurt Trump. I disagree with the rest of it. There is a whole generation of voters now who have never heard anything about Clinton contreversies from the 1990s.