When you create a viber account, you are asked to connect through social media like Facebook or Gmail. Although Viber does not track data from your Facebook account, it only connects you through Facebook.
The only information it takes from Facebook is your name and profile picture, otherwise, all data is encrypted and Viber does not take information from Facebook.
Viber uses the name and profile picture from Facebook. After making an account on Viber you can keep the same profile picture on your Viber as you have on Facebook or change by uploading from your phone gallery.
Its mean viber is connected with Facebook for only certain information but not get access to all post and data.