Aminadab’s message is that they must believe in the voice, and he identifies the voice as that of Christ. His next identification is problematic. He notes that Christ “was taught unto you by Alma, and Amulek, and Zeezrom.” This would appear to indicate that these particular Lamanites are of Zoramite heritage. At least in the text Mormon has given us, the only missionary journey with these three together is that to the Zoramites:
Alma 31:5-7
5 And now, as the preaching of the word had a great tendency to lead the people to do that which was just—yea, it had had more powerful effect upon the minds of the people than the sword, or anything else, which had happened unto them—therefore Alma thought it was expedient that they should try the virtue of the word of God.
6 Therefore he took Ammon, and Aaron, and Omner; and Himni he did leave in the church in Zarahemla; but the former three he took with him, and also Amulek and Zeezrom, who were at Melek; and he also took two of his sons.
7 Now the eldest of his sons he took not with him, and his name was Helaman; but the names of those whom he took with him were Shiblon and Corianton; and these are the names of those who went with him among the Zoramites, to preach unto them the word.
Of course, there may have been a different missionary journey that is not recorded, but it is also possible that these Lamanites are the apostate Zoramites. In that case, however, it simply indicates the great extent to which they Zoramites has lost their connection to the Nephite religion, as they were unaware at this time of the meaning of the scene they witnessed. It would appear that Aminadab was either a more recent dissenter.