Probably not. But much of the point of accepting submissions is to onboard submitters, right? You are investing in a human being and their ability to store and utilize institutional knowledge about your project.
If someone repeatedly contributes to the project, in larger scales, it will eventually become obvious if they use LLMs - people who do so don't really "turn it off" some of the time, once they're acclimated to these tools. This is mentioned in your own AI policy - the skill atrophy problem. So while some problematic contributions are small enough to fall under a practical, perceptual and legal radar, and that is a fact of life, problematic contributors do eventually reveal themselves, and you deal with the problem then. That may or may not involve review of their previous submissions according to human judgment.
Like I said, this is entirely analogous to previous copyright attribution problems.