Are the Polynesian people of Lamanite descent?
That appears to be the consensus among Mormon writers. Here is an exemplary paragraph from Encyclopedia of Latter-Day Saint History)—
“In the great final battle at Cumorah, as recorded in the Book of Mormon, the Nephites, who had become even more wicked, were destroyed, and the Lamanites were spared. These surviving Lamanites were actually descendants of both the original Nephites and Lamanites. Today Latter-day Saints typically identify American Indians, the indigenous peoples of Latin America, and Polynesians of the Pacific as “Lamanites.” The Book of Mormon speaks of the time when the “scales of darkness” would fall from the eyes of the Lamanites, and they would once again become a “pure and delightsome people” (2 Ne. 30:6). President Spencer W. Kimball frequently spoke of this glorious destiny.”