By the way, what are you trying to do... accessiong to SQL Server with SQL PLUS or any other Oracle Software???
And yes I would say it´s the only way however I think the gateway can only be used between an Oracle DB and SQL Server DB and not from an Oracle client to a SQL Server DB. You have to buy it, you can check technet for more information about Transparent Gateway.
I think you are looking for the gateway, the way it works is it will setup a database link between SQL Server and Oracle, then Oracle will treat that SQL Server as another Oracle Server. Although I am not sure if you could use snapshots. May be you should contact Oracle about gateway´s functinality.
I'm trying to replicate from Oracle to Sybase and vice-versa.
I tried to search for Transparent Gateway on technet and other websites for it, but couldn't find any details.
If anyone can send any links that would really help.