Ainus lived in fixed houses and farmed and fished, they didn't live in tents/yurts to herd livestock between seasonal pastures. Therefore, the Ainus were not nomads.

The Ainus were not restricted to Hokkaido, they also simultaneously lived in the Kuriles and Sakhalin (at the time called Ku Ye). They were not recent immigrants to that area and had been there for centuries or millenia before the Qing Dynasty was eestablished. What did you mean by "those people", the Ainu or the Yamato Japanese?

The Qing government had permanently stationed officials at the Heilongjiang mouth. They certainly treated that territory as if it belonged to them, along with its inhabitants, and successfully fought off Russian incursions there in the early years of the dynasty. At the time, the "small and dispersed" Daur, Evenk, and Nivkh tribes were nonetheless regarded as subjects by Qing and worth defending against Russia. Yakuts and other Russian-ruled people were not. Bottom line is, the Qing actually cared about which people were "their" people, and any Ainu living on Qing land (unlike descendents of Chinese emigrants who had forsaken Chinese nationality) and subject to the Qing government (unlike illegal Central American immigrants in the modern US, or the Russian and Korean subjects who would illegally cross the border to poach deer and ginseng during the Qing period) would probably legally be considered Chinese at the time (but not anymore, due to cession of the territory to Russia).