Is Oracle more demanding environment for a DBA than SQL Server?
Oracle has a significantly higher barrier to entry than SQL Server. Does that make working with Oracle "harder" than SQL Server, well that depends on what is meant by "harder" and where you're setting the bar.

I've very rarely encountered enterprise, Oracle backed systems, that didn't have dedicated Oracle DBAs/developers on the development team. I frequently work with SQL backed systems that have been developed without any DBA expertise whatsoever.

Why?

Microsoft are smart. They've built a database platform that competes with Oracle but made it accessible to anyone that can knock up a database in Access.  The notion of Code First, for anything other than the most noddy of departmental applications, scares me witless. But doesn't it make great commercial sense? 

Hide the complexity. Make it easy for anyone to build on your database platform. Later, once they're locked in, they can find all the knobs, levers and switches they'll need to get the best out of the product.

Oracle requires expertise on knobs, levers and switches before you can create your first table. To the novice, that makes Oracle more difficult to get started with. Not technically more challenging, just in comparison to SQL Server, plain difficult. 

If you're a developer that just wants to "get things done", which platform are you likely to lean toward?

Is an expert Oracle DBA more expert than his SQL Server equivalent? No.
Is Oracle technology more complex than SQL Server? No.
Is difficult or demanding a good benchmark for anything? Commuting across London on the underground is both but I don't feel superior for doing so :)