In theory. In practice, like Slack, Discord is unsearchable. As someone rightly said on another thread: Discord is where knowledge goes to die.
Until you train llm on it. Which WILL happen.
LLMs perform lossy compression on knowledge, so they're not a good replacement for indexing and search. If anything, you want to have the latter, and expose it to LLM as a tool it can use, regardless of whether the LLM was trained/fine-tuned on that same content or not.