Can the default login folders for FTP be changed? If so can this be done via the Control Panel
FTP Login Folders
no, to the best of my knowlege there is no way to do this on dreamhost.
edit: I should follow up with that a bit. You can set your FTP client to automatically move into a folder when you log in. But if you asking more can I have two users have access to the same domain, then the answer is still no.