Why would they need to be prepared? NaNo is on you, you don't get anything for winning other than satisfaction and online badges and stuff from sponsors, such as some promo codes for writing software and getting your initial draft printed.
A text that reads "Rabbit." written 50,000 times is enough to win NaNo.
As others have mentioned, since it's self-driven, this would not be a problem. Rather than viewing it as a problem, in fact, one could use AI to "ensure" they produced finished or clean pieces of writing.
I'm less in the frame of thought of using AI to "write a 800 word story on leprechauns" and more in the situation of "edit my lead paragraph in the same style as my concluding paragraph" or "here is an outline of my story, critique it and give me a structure to follow for a second draft".
As a self-driven exercise then, AI becomes just another tool for a writer to get better. Sometimes it's a training wheel, sometimes it's a rocket strapped to your butt.
The only "win" is personal and if you want to define your win in terms of ML/AI, that's for you to decide and mostly just between you and your keyboard. But there's a lot of neat resources and a different sense of accomplishment/competition/cooperation if you choose to focus on it as a NaNoGenMo project instead of a NaNoWriMo project.
Back when I did this, you could already technically "win" the pat on the back just by copying and pasting 50,000 words of gibberish to meet their word count. But then you would be cheating yourself: the point isn't truly to get the award at the end, but rather to challenge yourself to write 50,000 words in a month, to make novel writing seem less like an impossible task.
I remember there being a group out there that had the same competition but trying to tweak a good LLM to write a novel in a month, but I couldn't find it again and it was before the ChatGPT heyday.
Which I think largely pre-dates the availability of LLMs and is/was more aimed at traditional procedural generation techniques, although I imagine LLMs get used a lot these days.
From what I remember when I last tried it, NaNoWriMo worked with the honor system. If you wanted you could paste a wikipedia article in the editor and it would count the words and tell you good job, but you'd only be lying to yourself in the end.
A text that reads "Rabbit." written 50,000 times is enough to win NaNo.