The Boxer rebellion is important as in 1900 the Chinese peasents rose up against the foreigners in Peking and put almost 400 of then under siege in Peking in the foreign quarter. At that time a wave against Christianity and the Pastors and missionaries also spread across China.
I am not really concerned with the ethics involved, but the British who were the rulers of India at that time transported some 3000 troops to Peking. These were mainly Sikh and Punjabi troops and they reached Peking. They were officered by the British.
These troops went into battle and in hand to handfighting rescued the foreigners. Some of them also made use of the ancient sewage tunnels to reach the foreign quarter. The British Indian army also took away a large bell from the temple of heavenly peace in Peking. It is good that the Indian army returned the bell to Chinese army in 1994.
The battle and use of Indian troops to quell the boxer uprising is I suppose a sore matter with the Chinese. Perhaps some of the Indian troops also felt empathy with the Chinese, but they obeyed the orders and helped put down the Boxer rebellion. it is understandable that the India and China do not want to overplay the use of Indian troops in quelling the Boxer uprising.
The Indian troops were also used to guard the churches and the missionaries in China at that time as a wave of violence was unleashed against them. But all that is part of History. it is worth mentioning that the Indian troops were also used in the Opium wars with China in 1842.