Hey Kevin -
Desktop is the only supported way to create a data source, however TDS files are nothing more than XML documents, so you might be able just to take an existing file and "hack" it up a little. You'd be on your own here, though.
I'm not 100% sure what "all other access is locked down" actually means, but that could pose a problem publishing the data source TO Tableau Server, as well. We have a command-line tool called tabcmd which could let you publish the data source (TDS) to Tableau Server. When I use it to publish a SQL Server data source to Tableau, no connection is made to the database UNTIL the data source is used inside Tableau Server - which is what you want.
I'm not 100% positive that the same thing is true for Oracle (although I'd assume things are the same) since I haven't tested it myself. So you might get hung up on the publishing part.
When all is said and done, getting "blessed" access to the Oracle box via Desktop will be the easiest way to go