Hah I think of that South Park too. This might be the change with the most varied reactions out there. Completely separate from whether you like yub nub or not, some people think this song is beautiful and moving, others just think it's the worst. Supposedly Lucas gave Williams a temp version of the new ending with this music from a TV miniseries and said "sort of do this."

500 Nations (Powerful Native American music and art) - YouTube

The actual bootleg of the rough '97 version with that music used to be on youtube but it looks like Fox pulled it.