I doubt that it has ever been possible to obtain enough output tokens from OpenAI or Anthropic to be useful for training other LLMs.
In any case, had that been possible in the beginning, it stopped being possible long ago, because any suspicious accounts would be banned and the cost would be prohibitive even if they were not banned.
On the other hand, anyone can train new LLMs using the open weights Chinese LLMs, or the much fewer open weights LLMs with other origins, like the NVIDIA LLMs.
So in reality it is much more plausible for a US company to use Chinese LLMs for training, than vice versa.
In any case, had that been possible in the beginning, it stopped being possible long ago, because any suspicious accounts would be banned and the cost would be prohibitive even if they were not banned.
On the other hand, anyone can train new LLMs using the open weights Chinese LLMs, or the much fewer open weights LLMs with other origins, like the NVIDIA LLMs.
So in reality it is much more plausible for a US company to use Chinese LLMs for training, than vice versa.