Solution:
1. Go to Maintenance | General | Object Type | File Server tab.
2. Include the command (./.ssh/rc) in the ‘Post Login Cmd ‘ column in the File Server Tab for the object type
3. Log in on the Env on the File Server machine and modify or create the .ssh/rc file exporting the Oracle Envs needed by sqlplus, like
Export ORACLE_HOME=/…/…/
Export TNS_ADMIN=$ORACLE_HOME/network/admin
Export PATH=$ORACLE_HOME/bin:$PATH
4. Apply these changes for the object type, and perform a new migration.