Possible, but unlikely.

J. K. Rowling has made it known that Gilderoy Lockhart is the only character in the series to be based on a real person, and claims that she “barely exaggerated” the personality. She has refused, however, to specify who that is. Furthermore, she stated that basing the character on this man “made up for having to endure him for two solid years.”[44]

A rumour circulated that the character of Gilderoy Lockhart was based on J. K. Rowling’s ex-husband, but this was roundly refuted on her website. She termed the rumour “toxic”, “hurtful,” and “damaging”. Although it is not public who was the basis for Lockhart, Rowling inadvertently revealed it was not her first husband.

https://harrypotter.fandom.com/wiki/Gilderoy_Lockhart

The only character who is deliberately based on a real person is Gilderoy Lockhart. [Laughter]. Maybe he is not the one that you would think of, but I have to say that the living model was worse. [Laughter]. He was a shocker! The lies that he told about adventures that he’d had, things he’d done and impressive acts that he had committed… He was a shocking man. I can say this quite freely because he will never in a million years dream that he is Gilderoy Lockhart. I am always frightened that he is going to turn up one day. He is just one of those people from your past whom you feel you have never quite shaken off. I will look up one day at a signing and he will say, “Hello, Jo”. [Laughter]. Other people have contributed the odd characteristic, such as a nose, to a character, but the only character who I sat down and thought that I would base on someone is Gilderoy Lockhart. It made up for having to endure him for two solid years.

http://www.accio-quote.org/articles/2004/0804-ebf.htm

Edit: Also, given that L Ron Hubbard died in 1986, it is unlikely that J.K. Rowling would be frightened of him showing up at one of her book signings.