Connect analysis services to oracle database
How can I make SSAS use the tnsnames.ora file that I need?
  


The best answer is don't bother.  Use the Easy Connect naming method, and bypass the TNSNAMES.ORA file entirely.

Alternatively you can set the TNS_ADMIN environment variable to the folder containing your TSNNAMES.ORA file and reboot your server for the SSAS service to see get the changed environment.