I suspect most of us use one file server to store our music files. But, the predecessor code to Roon (Sooloos) supported multiple music file servers seamlessly. It appears that you can add Watch Folders that “point” to multiple file servers with no problem. Certainly right now I have four different Watch Folders (they are different file systems on one server, though).
The nice thing about Roon is that you can move files about, rescan, and it “remembers” the scanned information, and updates the paths when they are updated. A small example, 2 file servers, old and new, add some new files to the new server, tests fine, eventually migrated old files to the newer file server, rescan, and then consolidate to one server.