Yes, the source code is how I know "in-post" images are being served by the CDN but "featured images" are not.
The weird thing is that none of the images were being served until I added "{wp_content_dir}/uploads/sites/*" to the custom files list and now only some of those images are being served - even though they are located in the same folder. (Eg. uploads/sites/4/2014/02)