[tribe2012]

I've spoken to a former Googler that was on the search team, and he said the duplicate content isn't as big of a deal as one would expect. They realize when it is and isn't an issue. For example, blog reposts do not hurt you (in fact they may help you) even though they show up as duplicate content.

Just my 2 cents. I'm not a fan of WPEngine anyway.

[eli]

I would be shocked if there's any sort of duplicate content penalty for having two different domain names point to exactly the same site (same IP and everything).

[bhartzer]

There is actually no such thing as a "duplicate content pentalty". It's not a penalty. Google indexes (and cares about) whatever they crawl first: the other duplicates are pretty much ignored, even though they will show up in the index.