Hey there, rythmdoctor!
To clarify, slightly, Social isn't necessarily going to be connected directly to your MailChimp lists in your account. Instead, what it does is integrate your social media sites in tighter with your WordPress installation. In turn, it also can fetch replies to your post on Twitter or Facebook and bring those in as new comments on your blog.
Social isn't necessarily meant to add commenters to your MailChimp lists, but rather allow your viewers more flexibility when commenting by allowing them to log in as their Facebook, Twitter, or local accounts.
If we can help with anything else, give us a shout!