My understanding of the foundation year is that if you are predicted the grades to get a regular undergraduate place, you are not eligible. It says on the FAQs that it is for students who (due to disruption) “are unlikely to achieve the grades required to make a competitive application for direct undergraduate entry”. If you are predicted grades that could take you onto the main course you would be expected to apply for that.
If you have been in care, that will be flagged as part of your regular information and your application will be treated contextually. You might also be considered for the Opportunity Oxford scheme (for candidates who have experienced disadvantage but who are still on track to meet the entry requirements for their course).