NO! You don’t get it! They are part of the US. They are subject to taxes if we want to make them subject to taxes. It doesn’t matter if they say (when and if) that they have become a new nation or not. We can tax the hell out of them if we feel like it. They can jump up and down screamin’ all they want. It doesn’t matter. If you reside in the US, we the people have given the US Government the right to tax and if the US Government decides to tax the Lakota nation if it decides to, it can.
According to treaties SIGNED by the government of the US, no the US Government can not impose taxes within the borders described by the treaties.