Discussions do not get responded to as quickly as a case would for you though. Our support team does monitor these discussions, but the disucussion has yet to be assigned.
They will provide instructions on how to reconfigure. If you want more detailed instructions or a review of your sites settings, it would be more appropriate for a case.
Is your intent that the users will register and be active elsewhere within the community, or just the group? In Jive 7+, there is an option to enable 'Externally Accessible Groups.' This allows you to invite external users to a private group/space without having to register. Here is some documentation on Externally Accessible Groups. Jive 7.0 Community User Documentation. I don't believe this solves your issue, but it's another option.
Associate Technical Account Manager
Nick and I discussed his needs for this case. He wanted the normal invitation process from Jive, and to have users still use SSO to authenticate.
This is controlled via a system property invitations.system.enabled which needed to be changed to true.
This is noted in Undocumented Jive System Properties:
When TRUE, enables "invite user" functionality. When FALSE disables "invite user" functionality in UI and user wizard.
Which this now works for Nick and I confirmed that over the phone.