I'll speak on behalf of my past 18 months of working with several Jive customers.
The number one CMS I see used with - or intending to be used with - Jive is Microsoft SharePoint 2007. I've also seen Documentum, but it's mostly SharePoint. We have a few customers who are implementing Jive Connects for SharePoint to better facilitate use cases that span both applications.
What CMS is your organization looking to use in conjunction with Jive?
What about Kentico? Any Idea?