Migrate Organic Groups from a Drupal 6 database to Drupal 7
The migration classes that come with Organic Groups are for doing a full site upgrade only. In other words, if you were to drag Drupal 7 files over top of your Drupal 6 site and run an upgrade, the migrate classes that come with OG would be helpful.

However, in your case (and mine) you are doing a full migration from an old Drupal 6 site to a fresh, empty Drupal 7 site. The classes provided by OG will not be helpful here, nor even show in your migration list.

What I'm currently doing is working on a manual migration path for OG groups using migrate_d2d to pull all the group nodes over. Then I'll write another migration to add users to these groups by injecting them into the right database tables. THEN as each of my other node types are migrated over, they will add themselves to the OG tables that track which content are part of which group.