Yes, you can post to Secret Boards on Pinterest from Viraltag. After you connect your Pinterest profile under 'Accounts', and grant Viraltag permission to access your account, a 'Pin to Secret Boards' window opens up. Enter your Pinterest account credentials, and you're all set!
The next time you pin an image, you will find your secret boards listed as options in the drop down menu.
If you have already connected your Pinterest account and have not enabled pinning to secret boards, disconnect it in the 'Accounts' section. Then reconnect it by clicking on 'Connect' next to the Pinterest icon. The 'Pin to Secret Boards' window will pop up after you enter your Pinterest Login Credentials.