I am assuming that you gave him his own web id, and granted privileges to him?
He needs none of that for ftp. When you signed up you received an email, [yoursite 0000000) DreamHost FTP-only User Activated.
Just give him that user name and password. He can ftp using that. But not get into the web admin panel.
Now, if he needs to set up databases, then you can grant his new webid access to the Plans area. Or, you can set up the database and just give him access to that one particular database.
Chances are, when you created his own webid, something got chucked when you set up his user info.
When you ftp the new information to your site, yes, it is instantaneous…but sometimes I need to refresh my screen due to my cache.