It's important to keep in mind that in Pronto, you only see and have access to the groups that you are a member of.

What's made in Blackboard can only be modified in Blackboard. If a group or course is created inside of Blackboard, Pronto will not allow users to add new users or take away users from that group using the Pronto tool.

If users are added to the group through Blackboard, those users will be added into the group's Pronto conversation as soon as Pronto syncs with the system (about every six hours).