Do dreamhost allow users under a single account to have independent access to the control panel?
I think so.
But you may get better response at DreamHost forum.
Also, it's often quicker/easier to search their wiki.
Do all database and email account creation have to go through the control panel?
For e-mail, probably yes.
For a database, I'm not sure.
I guess you can create tables from script or mysqladmin type of utilities,
but maybe not for database.
Again, I think it's better to check wiki, forum, or their support.