Again james - see you still quibble on your terminology. Were you to bother to read Romans as I earlier indicated, you will find there that there is a universal witness of God - some call it general revelation. Since that knowledge is recorded in our scriptures, it is known to us as well as to that individual in the jungle who's never encountered anyone else. That is in the bible james.
They are "saved" by following that "inner voice" that they cannot name as Jesus
Show us your conclusion from scripture james - not your personal book of second opinions.
If these people are "saved" in such a manner, then of what use are the scriptures? Couldn't everyone be "saved" by "hearing" that "inner voice" and obeying it, instead of reading the texts handed down by mere men, and obeying the dictates therein - thus being forced to have faith in the accuracy of the conveyance from deity to prophets to men, before they can have faith in the deity, instead of direct telepathy from the deity itself, as these tribals did, thus being able to have faith in deity alone without the pre-condition that they have faith in what men have told them about the deity?
Sigh, since you want to entertain the prospect of a God in your construct, then you are going to have to accept a few other items.
1. Absent your documented "inner voice" scripture passage - your first condition is false. And I am not worried about this condition changing any time soon - your strawman here doesn't exist scripturally.
2. The condition of sin (a particularly hard concept for most atheists) is a condition of SEPARATION from God - a condition under which all exist. Adam and Eve (your original 'tribals') did relate directly with God - their sin separated that open communication. Your scenario is puny compared to that which God has laid out in the bible.
3. God chose his prophets to convey his message to mankind in a way they could understand. Since God chose to have his communications with man recorded in such a manner - God being God is able to preserve those communications, and that is what the faith is based upon. There is no "pre-condition" james, what is required is the initial recognition that the individual has sin in their life and that it has separated them from God.
4. But God didn't stop there james, He came down as God the Son - Jesus to once again deal with the sin issue personally. He validated what the OT recorded and his followers documented his actions and teachings.
Faith in a deity alone doesn't bring salvation james. Since you are attacking Christianity, at least spare the platitudes in that regard. Even within Christianity it is not faith that brings salvation - but is it God's grace extended to us through the sacrifice of Jesus. And for those who have heard, we have a name to associate with it - Jesus. And if your 'tribal' individual is saved outside of traditional methods of knowing Jesus - his salvation is still founded upon that same sacrifice. And example - People are not lost because they have not heard. They are lost because they are sinners. We die because of disease, not because of ignorance of the proper cure (Boa and Moody, 1982)
Atheists like you are so narrow minded when it comes to the grace of God revealed in the bible (and you have the nerve to call us narrow minded) when coming up with your little constructs. The bible tells us that who so ever seeks after God in truth will find him - that includes your individual tribesman james.
Muslims believe the same, too. Hence the "claim" that the Quran can never be corrupted.
There is no "pre-condition" james, what is required is the initial recognition that the individual has sin in their life and that it has separated them from God.
Again, this is your faith. However, there is NO WAY you can arrive at this conclusion about your chosen deity, without people telling you about this "property" of the deity. This is a problem that arises precisely because faith in a particular dogma and the associated deity relies on scriptural knowledge of the same, and is thus a pre-condition. You wouldn't be a Christian without having access to the Bible men have brought to you, would you?