You can’t really tell from Manage Users what domains the user has access to. Log in via the user that is listed in the “web hosting” column of "manage domain"s.
It’s not hard to use filezilla with dreamhost. http://wiki.dreamhost.com/FileZilla_Setup
To answer your question what are you missing, I believe it’s an understanding of how users are associated to domains. There is only one user per domain, a second can’t have access as your post above implies.