I haven't set up IMC with Oracle, but I have done it a few times with SQL Server.
I'm guessing that the Oracle approach is similar to SQL Server, where IMC wants to set up and configure all the individual databases and users it needs.
What we generally do is give full access to IMC when it goes through the initial setup, and then drop the privileges on that account. For normal operation it doesn't need that access, as each db has a new, dedicated account associated with it.
When you deploy new modules, or upgrades, you will need to add those privileges back.
Unfortunately there is no easy way to manually set up the databases - you have to do it through IMC.