Does WebLogic Custom Trust involve implicit use of Java Standard Trust?

We have an on-premises WebLogic SOA (12.2.1.4) instance that is set up to use Custom Identity and Custom Trust. The Custom Trust Keystore is set to a JKS file that contains 3 trustedCertEntry objects. All of the trustedCertEntry objects are internal network certs.

The WebLogic SOA instance is successfully invoking an internet https API that is using a cert issued by a CA under DigiCert Global Root CA. The same SOA instance is also successfully invoking internal APIs where the trust path relies on the trustedCertEntry objects in its Custom Trust Keystore JKS file. There are 'Loading trusted certificates from the JKS keystore file ...' lines in the server logs.