On the latest release of Mac OS X (El Capitan), the DYLD_LIBRARY_PATH environmental variable can no longer be set meaning that connections via a OCI/Thick driver (Instant Client etc.) cannot be used. There are open radars with Apple on this issue but no one is sure if this is temporary or an intentional change for security reasons. It would seem wise to move away from any kind of environmental variable use on Mac in the long term.
This has highlighted an inconsistency with SQL Developer. After extensive testing, I see that the property, java.library.path is used for finding the OCI drivers during startup (as confirmed by checking the sqldeveloper.oci.available property). I forced the setting of java.library.path using startup parameter AddVMOption -Djava.library.path=/path/to/instantclient. However, when it comes to actually using or testing the OCI connection, it seems that java.library.path is ignored and DYLD_LIBRARY_PATH is used exclusively whereupon it then fails because it is unset. All OCI driver paths should be obtained from java.library.path in order to fix this issue for Mac users going forward. All testing done using SQL Developer 4.1.1. All of the above works fine on the previous release of OS X Yosemite.
Please check it out. Thank you.