If model weights aren’t copyrightable, derivative model weights are not a “work”, derivative or otherwise, for copyright purposes.
If they are, and the license allows creating finetuned models but not using the output to improve the model, then the derived model is not a violation, but it might be a derivative work.
At the end of the day it's not black and white, but there's a large and obvious difference in degree that would plausibly permit someone to find that one is and the other isn't. It's fairly easy to argue that using the outputs of LLM X to create a slightly more refined LLM Y creates a derivative work. The argument that a model is a derivative work relative to the training data is not so clear cut.
If they are, and the license allows creating finetuned models but not using the output to improve the model, then the derived model is not a violation, but it might be a derivative work.