If I understand correctly, this is what I do when I am scrambling together with a beginner or with someone I am not sure of how good they are at scrambling. If they finish a scramble about the same time as I do, I quickly glance at their cube. Of course I can't check all of their scrambles since I can only check when I just finished scrambling a cube myself, but it certainly helps and motivates the co-scrambler to check themselves and scramble carefully. Encouraging this is a much better way of dealing with this 'problem' than having extra people to check the scramble.
Why don't you list all cases so we have a clear base to start from in the first place?
You are suggesting that the writing of the current regs don't make it clear that the scrambler is responsible for scrambling right here. I disagree. How would you change the writing though?
I think we are jumping to conclusions and not-thought-through-proposals without fully exploring the cause and magnitute of the problem and the possible ways to solve this. There are many other, way more practical ways like I described above to encourage scramblers to take responsibility and actually do their 'job'. We really don't need a scrambler-police for that.
Also: the good thing is, is that events where scrambles are a big influence (2x2, Pyraminx, Skewb), the scrambles are very short so the risk of misscrambling is smaller than at 7x7 (where the scramble barely matters).
Your claim is vastly exaggerated, but yes of course there are cases that are not noticed. There are numerous other things that probably didn't get noticed (like wrong delegate/judge decisions). Incidents happen. That's inevitable without WCA-provided staff for all posts.