Hi Richard,
We tried on the site and added the code in a custom plugin.
When under Author's New Post Screen, author cannot select which Publicize channel (as it is not displayed) So we thought it worked. After we hit publish the post to post a test article.
It was publicized to all the Publicized connections we set up in while in Admin role.
So seems like the code above is not preventing Author's post from being Publicized.
Like you said it is untested. Hope you would be able to try it out and see if the same result occurs on your test.
Thanks