Siu Fung became sworn brothers with both Yeh Lut Hung Gei, the Emperor of the Khitan Liao Empire, and Yeun Nan Akuta, the chieftain of the Jurchen tribe that would, a few decades later, conquer the Liao Empire and found the Jin Empire.
Given Siu Fung's personality and inclinations, it's likely that he didn't think twice about becoming sworn brothers with the leaders of the Khitan and Jurchen peoples. I wonder if Siu Fung was even aware of the conflict between the Yeh Lut and Yeun Nan clans, a conflict that was still active 130 years later during the timeframe of ROCH.
Interestingly, Siu Fung's sworn brothers included the rulers of the Liao Empire, the Jin Empire, and Dali Kingdom.