Since there was no response to this...
the answer is under Shutterfly's Help Center page, which states:
"Updated 02/01/2017 12:03 AM - Shutterfly currently does not support file storage services such as Google Drive, Dropbox, or FTP, and does not have plans to do so in the future. Please see our list of upload methods available to add photos to your account."
You can read it on their Help Center page
Available upload methods: https://support.shutterfly.com/app/answers/detail/a_id/51
Hope that helps.
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