““God, who made the world and everything in it, since He is Lord of heaven and earth, does not dwell in temples made with hands. Nor is He worshiped with men’s hands, as though He needed anything, since He gives to all life, breath, and all things. And He has made from one blood every nation of men to dwell on all the face of the earth, and has determined their preappointed times and the boundaries of their dwellings, so that they should seek the Lord, in the hope that they might grope for Him and find Him, though He is not far from each one of us;”
Acts 17:24-27 NKJV
God is omnipresent, omniscient, and omnipotent. Indigenous people are probably more spiritual than a lot of people in the modern world because they live in raw creation with little distraction. I've encountered God in my dreams on multiple occasions, I know he's capable of reaching indigenous people that way as well. Those people are required to respond to whatever message God has sent them in the absence of the Gospels. Those people aren't rejecting Jesus and will still receive salvation since Jesus and God are one in the same. The Gospels will reach all nations eventually and Jesus will return soon after. I think people that have heard the Gospels and reject them should be more worried than those indigenous people. The answer to any obscure subject can be answered by the clarity of God's character. Why would a loving and patient God punish someone who is blameless? He wouldn't.