For instance, the Việt Cộng fought the United States and South Vietnamese governments while being both outnumbered and outgunned, but still emerged victorious in the end through primarily guerilla tactics. However, the Native Americans resisting Andrew Jackson's Indian removal acts whom were under similar disadvantages lost terribly.
My question is why did the Native Americans not succeed in employing the very guerilla tactics they helped the Americans invent for use against the British in the first place? What made the Việt Cộng superior in guerilla combat?
It's worth remembering that it wasn't the PLAF that ended the Vietnam War (if we count this term to signify the period between 1955 and 1975) - it was the People's Army of Vietnam (the North Vietnamese Army). Unlike popular perception, the Vietnam War was more fluid in its asymmetric nature; it ranged from classic guerrilla warfare up to conventional warfare and everything inbetween. Needless to say, the final '74-'75 PAVN campaign was conventional in every way of the word.
The question here should rather be: Why did the United States lose? I've written a large post on this topic previously out of a military perspective, which you can find right here. Also see this post.
If you have any particular questions, feel free to ask. :)
Later native resistance groups did employ strategies that resemble those of modern guerillas, most famously Geronimo. The Apache were not able to 'win' because of competing attrition losses and the dramatic reduction in their freedom of operation Americans were able to achieve.
By the time of Geronimo, the Apache had been involved in anti-colonial warfare for hundreds of years and the victims of (at least) dozens of plague outbreaks. Their methods were designed to minimize their own losses, but the US and Mexico vastly outnumbered Apache on every front. Geronimo at his surrender had fewer than a hundred warriors, while the VC commanded hundreds of thousands.