If anything, it should work perfect. Give it a bit to update throughout the web and try to ftp into yourdomain.com again and see if it works. the dns itself just tells the web that you domain is to be called by the dreamhost nameservers. once the dreamhost nameservers take over everything dns related is then controlled by dreamhost, and since they make it available in the panel, you.
normally, your ftp into is yourdomain.com with your username and password. i dont remember far enough back to remember if dh sent me an ip to ftp through until dns updated. but if your dns wasnt updated, and you were logging into your domains ftp, you were logging into whatever your old host had setup, not dreamhost.
as i said, the nameserver is what tells your system where to go to get the records for whatever your looking for. then you end up there. so unless you were logging in through your sites ip address from dh, or some other method besides yourdomain.com, chances are you werent in dh.
im goin to bed now