I work for an IBM business partner and this reply is
based on my best understanding of the current LotusLive Notes feature
set. It's not an official IBM answer.
My understanding is that all directory data referenced in both the Hosted and Hybrid models is handled internally by LotusLive in LDAP format (even if its original source was a Domino directory). Therefore, I would be surprised if either environment allowed you to selectively limit who can send to particular groups. However, the best way to get a definitive answer would be to engage with IBM or a business partner to begin planning a LotusLive deployment.