I looked up Nehemiah Gordon, but I'm a bit confused on if he is a Jew or a Messianic Jew, or a Gentile masquerading as a Messianic Rabbi. His store seems to have books which focus on the intersectionality of Hebrew and the early Church -- an odd field of study for a typical Rabbi. He also seems to be into hocking his own wares and stuff like the 1oz silver commemorative rounds.
I also wonder if his sources are Kabbalistic in nature, as those folks tend to go in all sorts of wild directions; or if he is finding bits and pieces of things to force fit his own theories.
Yeah, I don't know anything about him apart from what I've seen in the video. But in the video he presents himself as a messianic Jew. (I'm giving him the benefit of the doubt that he's not a fraud.)
If you haven't seen the video, his basic claim is that he's some sort of a researcher who has access to a database of obscure unpublished Hebrew manuscripts, and, using the database, he has found ~16 sources which all point towards this idea that the vowels were deliberately hidden, never lost. He says that scholars aren't aware of these sources, mostly because scholars aren't looking in the right place, and partly because these sources weren't always widely available (most of the manuscripts were never published--not even in Hebrew--, and some weren't even added to the database until recently).
There could be some truth in it: I don't doubt that there really are a lot of manuscripts out there which aren't widely available ans which may have been overlooked. And I don't doubt that Jewish rabbis probably have all sorts of obscure oral traditions which most people don't know about.
At the same time, it's all very sensationalized. (Nehemiah Gordon keeps saying that he's the 'first person' to make any of this stuff public. And then he goes so far as to claim himself to be a distant descendant of King David!) So it's possible that he's some quack who has no idea what he's even talking about, or else some liar or conman who is making stuff up and trying to profit off his 'research' via the publicity.