When an applicant is submitting a pre-screen or self-tape audition to a job poster, they may be asked to read private or copyrighted materials. Due to this, it is important that when sending in videos that have been uploaded from a 3rd party site that the ability to view these is limited to yourself and the requester. YouTube offers an "Unlisted" option and Vimeo a "Hide from Vimeo" option that would serve well in these cases.
If a video is listed as "private" it would not be able to be uploaded to Backstage due to the fact that private videos cannot be embedded to other sites. That is where the "unlisted' option comes in. If the video is "unlisted", it would not be able to be found in YouTube searches, but can be embedded to other sites and viewed by the recipient. For instructions on changing video privacy settings on YouTube please see here.
Vimeo "Hide from Vimeo"
Vimeo offers 5 different public/private settings with a separate set of embedding options. For the purposes of audition submissions, the "Hide from Vimeo" option makes it that the video will not appear in Vimeo searches, but can be embedded on other sites and viewed by the recipient. Information about this can be found here.
The Other Option...Direct Uploads
You can also simply upload media files directly on Backstage instead of using YouTube or Vimeo. This can be a great option for fulfilling pre-screen and self-tape audition requests. And as long as you don’t also add the media item to your public Backstage profile, then only you and the production/employer you’ve submitted the media to will be able to see it.