As someone who started out as an Oracle DBA (15 years) and got a later job as an SQL Server DBA (now I do both), it's really one-way. The benefit of being an Oracle DBA is you learn TIGHT code (semicolons matter) and adherence to syntax (Microsoft plays fast and loose). The engines are completely different, however, and as Brent points out, they're only marginally comparable. For example, Views on Oracle are AWESOME. Not so much on SQL Server. Also REDO vs UNDO - HUGE difference! TOP vs ROWNUM. Transaction handling (explicit vs implicit COMMIT). And database nomenclature... but what's in a name? I'd hire an Oracle DBA into an SQL Server position, sure. I would be skeptical going the other way, however. To much to UNLEARN.
I moved from being an Oracle PL/SQL developer and performance tuner to being a SQL Server administrator and T-SQL developer. It took some time to get up to speed on the differences, but I became effective quickly. It took much longer to get really good at it. Some of that was the database differences for performance tuning and some was learning database administration. It depends on what specific tasks you'd want to hire an Oracle person to do in SQL Server. Performance Tuning is going to have a long learning curve. Writing code, not so much.
