Whether you need to gather file evidence for managing sub-capacity licenses will ultimately be determined by whether the applications you have deployed under that license model are recognized in the ARL using file evidence, or recognized using some other sort of evidence (likely installer evidence). Most applications in the ARL are recognized based installer evidence, but there are exceptions.

Of course, there is a potential chicken-and-egg problem here: unless you have the evidence, you may not know what software you have deployed, and so you may not know what type of evidence you need to gather. As such, gathering file evidence as part of your inventory is the safer/more conservative approach.