Actually its a simulator, not an emulator. The simulator runs specifically compiled x86 code and simulates most of the iPhone.
Originally Posted by Jellotime91
An emulator would emulate Arm code and run the direct iPhone binary in the emulator (Android has this.)
Thus you cannot take an Arm binary on the iPhone, put it on the Mac, and run it in the SDK simulator.
If some developer wanted to go through the trouble of writing a true emulator they would have to include the full iOS runtime functionality in it and I am sure Apple legal would have a few issues with that.
TL;DR: No, you cannot take an iPhone app and run it on your Mac.