No, he's a liar. Firstly:
1. Inconsistent story:
If you look through some of his old interviews, he has made several amazing claims that are not mentioned in his new Netflix documentary or his interview with Rogan. For example, there's an old YouTube clip where you can hear Lazar claim that he witnessed autopsy pictures of alien corpses and gave a detailed description of their anatomy.
With Rogan (and elsewhere), he only claimed to “catch a glimpse” of something that might have been an alien through a window. Why didn’t he mention these autopsy reports? Because he’s a liar who can't keep a consistent story.
2. Holes in his backstory.
He was publicly asked when he got his MS from MIT. He said “Let me see now, I think it was probably 1982.”
Nobody getting an MS from MIT would not know the year immediately.
He was asked to name some of his profs, He said: “Let’s see now, Bill Duxler will remember me from the physics department at Caltech.”
The trouble is, Bill Duxler was a Pierce Junior College physics prof, and never taught at Caltech. Apparently, Lazar was registered in one of his courses at the same time that he was supposedly at MIT! Nobody who can go to MIT goes to Pierce JC, not to mention there's a fairly long commute between LA and Cambridge, MA...
3. Weird Physics
Lazar claims that element 115 has some exotic properties not seen in ordinary matter, that make it possible to use it to bend space-time in a way that gravity can be used as a propulsion mechanism. This in itself is a complete violation of how gravity works in Einstein’s theory of relativity and the standard model of physics.
However, if it was true then that means that there is a secret group of U.S. physicists that have uncovered evidence that all of modern physics is fundamentally wrong, and presumably have developed some alternate model of how the universe really works that fits with this alien technology. Therefore, all ongoing research in modern physics around the world into things like string theory or other fields should be thrown straight out the window, and all textbooks rewritten with this new knowledge.
For some unknown reason, they have kept quiet about all of this for over 30 years now...
Also, there's a clip on YouTube where Lazar is talking about “gravity A waves” and “gravity B waves” inside atoms to explain the properties of element 115 that make it possible for it to bend space-time. This is completely made up terminology that doesn’t exist anywhere in real physics. Anyone with even a just basic understanding of modern physics would know this.
Still, I'm sure plenty of people want to believe, so go ahead. I ain't holding my breath.