Doing a quick PoC, I've had to spin up 11g on very short notice. While anarchy is fun, I typically prefer a more guided approach.
Despite not reading documentation ahead of time (much), there is a method to my madness. I learn best by breaking stuff...multiple times.
So, there I am, fresh from exporting from Discoverer then migrating that RPD from 10g to 11g...configuring the Connection Pools. I select a random table and then hit View Data.
Awesome. Very descriptive.
I tried using the BI ODBC Client tool to test the connection.
Using the Google Machine, I found this reference to Visual Basic (is that really still used?).
Let's try looking something else up (like the documentation you say?). Actually, I didn't find it, a colleague did.
Over on the Siebel Essentials blog, tip #4 for OBIEE 11g, Connections.
To sum it up, you can either use the tns entry as the Data Source Name or you must put a tnsnames.ora file in the <ORACLE_HOME>\OracleBI1\network\admin folder.