I'm using the MusicSequenceFileCreate function to save out a midi file to make sure the data is correct. I'm not getting any errors but I would like to view the saved file but have no idea how to do this.
I know I can try reading it in in iOS but I would like to view it (and test it) on the desktop.
Is this file stored in some Simulator cache that I can access?
Yes the you can access the Simulator files from ~/Library/Application Support/iPhone Simulator/.
In this folder are the various iOS version numbers so pick the one you are running. In that will be Applications and you'll see a bunch of GUIDs, one of which will be the running app.
One thing in OSX 10.7 is that the Library folder is now hidden. This article explains how to restore the visibility; Show User Library Directory in Mac OS X 10.7 Lion