Forgive me for entering in the middle of this talk, but I would like to say that perhaps the answer is in the build logs.
I'm not giving a definitive answer like "Yes, it's non-free software", or "No, it's indeed free software". Quite the unusual: I'm trying to provide pointers to where the answer might be. Regarding the build logs, it might sound useless, but three months ago, I happened to find the build logs from the guys of the Linux-libre project in it's own repository. While the build logs alone don't give us much information, we could compare these build logs with a specific file (which I don't remember the name or location) from the copy of the Linux project source code that is being used by the Debian project. This "specific file" is supposed to tell the reader about the modules being distributed in the copy, along with the license and where their source code can be found in Debians' copy of the Linux kernel's source code.
