EBS OID AD DIP 12C

We have a requirement of integrating AD with EBS through OID and OAM 12c with EBS 12.2

Usernames in AD and EBS are different.

userprinicipal name in the AD are not proper format like not email,or emp.

Its customized for different & each user.

we are in the initial phase of the project .Ebs has already gone live .

But still we have not integrate the EBS WITH OAM.

we are planning to set Rtn as uid .but can we set also cn but not sure what advantage its brings

Questions:

1.Do we have to make the usernames same in AD and EBS for this integration . what if the user already created in the EBS .