A question that pops up on the OBIEE OTN forum quite often is how to use non-Oracle databases like MS SQL Server when the OBIEE server is running on a non-Windows OS such as Linux. The answer in a nutshell is that since version 10.1.3.3.1 OBIEE has been bundled with ODBC drivers for unix/linux from a company called DataDirect. See the release notes here for more information and installation instructions (as well as a list of support databases).