I worked at a place that tested software releases on a VM of every supported operating system, including OS X. We didn't have any Apple hardware, because no one wanted to deal with that, but someone had brought in the chassis of an old Apple computer and the host computer was inside it. We didn't run it by any lawyers or anything, but as far as we could tell, running OS X inside a computer that had all of its guts replaced was entirely within the license requirements.