OIM is an Identity Management tool to provide User Management, Self-Service, Password Management, Delegated Administration, Provisioning/De-provisioning...etc and does not have Access Management capability whereas OAM has got Authentication/SSO/SAML capabilities.
I believe your requirement is to integrate CA API gateway with OAM for Authentication/SSO. CA APIM can be integrated with OAM and it is supported as per below article.
Requirements and Compatibility - CA API Gateway - 9.3 - CA Technologies Documentation
Identity Provider | Supported Versions |
Oracle Access Manager (OAM) | 10g, 11g |