Yes, license codes are valid on both the Macintosh and Windows versions of the software.
In fact, if you own both a Macintosh and a Windows computer, you do not need to purchase 2 licenses. You only need to purchase a single license. You may use the same license on both computers as long as you will only use one computer at a time. In other words, a single license entitles you to run one active copy of InqScribe.