Is there a directory of mods on Steam but not on TESNexus? If so, is there a convenient way to download them and still use Wrye as the main installer?

I use NexusModManager for download and version control, and Wrye for installation, load ordering, merging, etc.

Since there are over 25,000 mods on the Nexus and around 15,000 on the workshop, it would be pretty dang impossible to keep track of which ones on the workshop weren't on the Nexus...

There is a way to get Workshop mods into WryeBash - some sort of option for 'monitor Data folder', then download the mod from Steam, & Wrye will notice the new mod as a change. I don't remember the exact phrasing on the options but it is doable.