Pretty implausible, that would be a huge ship based migration that would not go unrecorded. the truth is that most were absorbed by Assyria and most of the rest absorbed into Judah.

Though the Lemba are interesting, they are just as easily later refugees from Judah from the Babylonian or Roman invasions. In the book of Acts, there is a person from Ethiopia reading Jewish holy books who converts to Christianity.

Most of the plains Indian tribes were monotheist though, and if they had struck up a religious conversation with a Christian who didn't know much theology, it would have taken them some time to realize they weren't talking about the same thing. The 'Native American Church', famous for rituals involving Peyote, identifies as Christian but I think generally believes they always were.