Which of the taiwanese indigenous tribes celebrates the illisin spring festival performing a dance where the men join together and move in a spiraling circle, while singing prayers for an abundant harvest?

I believe the answer is : Amis

In their traditional belief, The celebration of the festival is being done as a form of prayer towards God so they could get good quality harvest during the season. The "Harvest Festival" of the amis group is held during July, August, and September.