I have the same issue, however I found sort of a work around if you have the seamless settings configured:
Location in Windows VM:
The path is \\Mac\Home\Library\Mobile Documents
The folder names are a bit cryptic but have some abbreviated form of the app that created it...i.e like "COM~apple-notes" or "iCloud-com-Applejacks".
Tested:
I opened, modified and saved files in Windows and they sync'd live across platforms (a markdown editor open on iOS, Mac and Windows at the same time (had to refresh doc on iOS to see change - Mac and Win apps showed the change immediately without even closing the doc).
Manually browsing:
1) Browse to desired icloud folder in OSX Finder,.."right click" (haha) and select "Reveal in Windows" (last option in list - Parallels added option).
2) Windows VM - an Explorer window opens and shows the path contents which you can then shortcut or quick access to.
Last edited: May 18, 2018