Hi Hugo!
Lotus Notes/Domino does offer support for LDAP (it can expose the users in the Domino directory to Jive via the LDAP task), so that would be the first avenue I would check out for the single sign on part.
For publishing content from Notes to Jive SBS:
The easiest way is probably the RSS Feed Generator that comes with Notes/Domino 7.0 and up (the template is called RSS Feed Generator (rss_generator.ntf) and is available as part of a standard domino install. It allows you to publish any Notes View as an RSS feed, which you can then consume within Jive.
Those are the standards based integrations that come to my mind. I'll also check if colleagues have done additional work in this space.
Of course if you have specific needs you can always use the Lotus APIs to build things. Before making a suggestion here I would like to understand your requirements better. Feel free to contact me.
Nils