I think there’s a big misunderstanding here. There is no “invisibility” of directories that begin with a period in their name in Windows, that’s a *nix thing. There is nothing special needed in IIS to allow a directory that starts with a dot to contain content pages which get served via http/https. Saying there is a problem with IIS serving a file that is located within a directory path that starts with a period is an error, because this is not prevented even in a default setup of IIS.
The issue, outlined above, is that IIS by default will not serve any files with extensions that it does not know about. Such as filenames without an extension at all. As an example, it does not know about .woff files (special font format) or .svg image files, so you have to add a mimemap for those also:
<mimeMap fileExtension=".woff" mimeType="application/font-woff" />
<mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
Without these mappings IIS will give a 404 error for those file types. I don’t know how much he knows about IIS configuration, but perhaps he is expecting to use a browser and go to that directory to see the files listed? By default IIS will not display a directory listing for security purposes; that has to be specifically enabled in the settings. And, again, MVC is a whole 'nuther thing.
The nuclear option would be RAMMFAR (Google it) but I highly discourage that…there’s always another way. Also, if he is running URLscan then that could be the culprit too.