Does LensCorrection only work with rift plugged in?

That is correct, there is no lens correction unless you have a Rift plugged in. This is because the Unity integration is querying the Rift for distortion coefficients so that it knows what kind of lens correction to do. If you need to see what it looks like without having a Rift handy, you can temporarily modify the OVR script code (somewhere) to return hardcoded coefficients (and a hardcoded distortion scale). I'm not at home so I can't recall the specifics, but that's basically what I did for a month or so before getting my Rift.