You dunno need root access to mysql, but you have to have access to the other database as well ..
So if your hosting only gives you one database you have to mix, there is no other way, but yes, that?s the way it is ..
If you have root access for yourself you can change the access level with grant and revoke for every database itself ..
Giving root access to any config file is a security risc ..
Bcz with that password all dbs could be deleted !
But usually root login to mysql is only allowed from localhost so it isn?t that problem to use root, but I would sugeest to NOT use root for any PHP program !