Only domains that aren't managed by Gmail show up in the list above the "Gmail-Managed Domains" section.
And I know they haven't been purged as I and the users still have access to them via webmail.dreamhost.com
My understanding is that Dreamhost will not purge these old accounts so that people can have access to their previous email after the switch over.
I wanted to try the Forums before contacting support as I know they're busy, and this is a relatively minor issue. But, I suppose that's what I'll try next.