Can I use more than one source for different parts of my business?

Yes. A typical use case  is to obtain the majority of rates via market rates then specific currencies or pairs via one or more central banks to meet local statutory requirements.

You can either overwrite specific market rates with central bank rates, or vice versa. In Oracle E-Business Suite and Oracle ERP Cloud, you also have the option to load rates from these different sources into different rate types, then configure your application to use these rate types where they are needed (e.g. by operating unit).