Short answer, no, each array drive is a single volume using all available space.
Long answer, Unraid is linux based, and the paths are going to be completely different between a windows and linux install of plex.
Disclaimer, I am an emby user, so I don't have first hand experience with this, but here is supposed to be a guide of sorts.
https://support.plex.tv/articles/201370363-move-an-install-to-another-system/