No disclosure for LLM-generated patch?

Another interesting question is whether the Signed-off-by line can be considered valid in this case, since I don't think any reasonable reading of the DCO would apply to LLM-produced code.

You didn't write it yourself, you don't know in what manner it was based on previous works (or their licenses), and even if you argue that the LLM directly gave you the code (despite not being a person), the LLM cannot certify the licensing status of the code (and would probably refuse to do so, even if asked).