Simple Permissions a plugin for WordPress by george_michael checks a users group membership when getting posts, so if a user isn’t a member of a group and that group is the only group that can read the post, the user won’t see it in a list view (admin or regular) or a direct link.
If a user is a member of a group that has the write permission to a post, but that user does not have a WP role that allows for editing that document (a subscriber, for instance), they won’t be able to edit it. Also, authors and admins are not group limited. If you wrote it, you can edit it. If you’re an admin, you can edit it.