So I have been trying to follow the Yammer Dynamic groups story, and I'm still a little confused. In order to take advantage of Yammer Dynamic groups, do you need to also be using Office 365 groups? Do you need to have Outlook groups enabled? Or, can you just use Azure AD?
Yes. The Yammer group must be connected to O365 before its membership can be changed to have dynamic membership. You must also have a license for Active Directory Premium to use dynamic membership rules with Office 365 groups.