You're always allowed to use any resource without permission if it is to be used privately and not published.
WFaS has pretty much always given permission to use their resources. In fact as long you credit them I'm pretty sure you're allowed to include it's assets. As you can see in an OSP Wilhelm made who's thread is on Taleworlds. In that OSP he made use of WFaS assets. So downloading that, you as well download WFaS content. Thus you can use it.
Just give credit.