We recently migrated to GApps sat work, and this is exactly how we imported old mail, so the feature is definitely there. I'm not sure if it's only available for GApps users or only available during some unspecified migration period, though.
It's only available to GApps users in the Admin panel. And when I tried it I had about 30% of my email missing in Gmail, so the import misfired. I ended up copying email manually with an email client. Maybe they fixed it, as I says, these days I'm on FastMail. But it's still a pita that the import has to be handled by admins.
