I can't image what reviewing C code like that would look like? Rust is a complex piece of technology, is the transpiled C code 'clean' enough to be able to review it?
It certainly isn't. Getting even C code written by human with best effort for addressing standards and conventions accepted is challenging enough.
This violates the GPL.
It doesn't, because C code is clearly "the preferred form for modification" by C kernel devs that, by their own admission, are quite unwilling to deal with the perceived complexity of a multi-language code base. (Or even to learn any other programming language, for that matter.)