Take a dummy organization that is used to avoid taxes. There is nothing illegal to pay someone to form a company located in a different country. A company can also sell assets to an other for what ever price they want, and there is nothing illegal to declare that as a result one of the companies now have zero profits and zero assets.
But if something is legal or illegal depend more than just on each set piece. If combining a blob with the kernel creates a derivative, then just adding a shim to the mix won't turn it legal. Judges are trained to look at the big picture rather than the individual parts, and this is especially true in civil-law. Court systems are generally interested in:
What is the kernel authors intention by their copyright license.
What is the blob authors intention by their copyright license.
What is the distributor intention when combining the two works and what understanding did the distributor have about the other copyright authors and their wishes in regard to derivatives.
The existence of a shim that has no other purpose is a sign that something shady is going on, similar to dummy organizations. The question a judge is likely to ask is why such obfuscation was used since that can help establishing intention. If the end result is a de-facto derivative, and the intention was to create a single work out of two seperate works, and the creator knows that they are not allowed to create a derivative work, then a shim is not going to save the day.
"Take a dummy organization that is used to avoid taxes."
See, that right there is where the analogy falls apart. Tax evasion is (usually) illegal. Writing software to translate between two independently-developed programs is not, last I checked.
"If the end result is a de-facto derivative"
You'd need to prove the blob is derived from Linux. If it's not, then there's literally nothing illegal happening here. If it is, then - again - the shim is not the illegal thing; the blob is, and the shim is entirely irrelevant in that illegality.
The usual reason for the shims, by the way, has very little to do with licensing terms (at least not directly) and very much to do with the fact that Linux does not provide a stable API (let alone ABI) for kernel modules. The intent of the shim is therefore almost always technical rather than legal in nature.
But if something is legal or illegal depend more than just on each set piece. If combining a blob with the kernel creates a derivative, then just adding a shim to the mix won't turn it legal. Judges are trained to look at the big picture rather than the individual parts, and this is especially true in civil-law. Court systems are generally interested in:
What is the kernel authors intention by their copyright license.
What is the blob authors intention by their copyright license.
What is the distributor intention when combining the two works and what understanding did the distributor have about the other copyright authors and their wishes in regard to derivatives.
The existence of a shim that has no other purpose is a sign that something shady is going on, similar to dummy organizations. The question a judge is likely to ask is why such obfuscation was used since that can help establishing intention. If the end result is a de-facto derivative, and the intention was to create a single work out of two seperate works, and the creator knows that they are not allowed to create a derivative work, then a shim is not going to save the day.