May I use a Microsoft Office for Mac license (SKU) to cover a Microsoft Office for Windows installation?

Yes, you may do that as long as the respective Microsoft Office for Mac license was purchased through a volume licensing program. In this case, Microsoft Office licenses are considered platform-independent. However, you may only install a software product in the same or a lower version compared to the version you are entitled to by the license (SKU).

Source: Volume Licensing Brief_Windows and Office with Mac_as is 2016-11-02