You can choose one..
If you using EBS 12.1, you can only use Oracle Internet Directory.
If you are using EBS 12.2: you can use Oracle Internet Directory or Oracle Unified Directory.
Read the following (you will find more questions and answers there) ->
https://blogs.oracle.com/ebstech/post/oracle-unified-directory-12c-certified-with-oracle-e-business-suite-122Quote: "From the perspective on an E-Business Suite end-user, both directories offer the same functionality, namely, end-users can log on to the E-Business Suite. The choice really depends upon your user directory administrators. You should use the one that meets your user administration requirements the best."