This does work, and I used it to point OneDrive to my Synology NAS. However, there is a caveat.
If (when) your OneDrive account becomes disconnected and you reconnect, it will look to the directory with your symbolic links in it and decide if the local drive the links are located on has sufficient space for the files in your NAS location. If not, it will present you with a message about negative disk space - see image Negative Disk Space and won't allow you to 'Next' .
You can, of course, deselect files and folders to sync, and continue. You will be able to access the files through the OneDrive folder, but new or changed files won't sync, which does rather defeat the purpose of OneDrive!
For you to recover from a disconnect, your locally declared OneDrive location must be larger than the file space occupied by your files in your actual NAS location.
I overcame this problem by moving my local OneDrive location to a drive that had more empty space than the files occupying my NAS. To do this I created a OneDrive directory on a 2 terabyte internal drive and recreated the Symbolic Links from my original OneDrive location in it (I didn’t want to risk a copy or move of the existing symbolic links in case something untoward happened as a result). Then I unlinked OneDrive from the PC via the Settings in the OneDrive app.
Restarting the app prompted me to log in and then accept or alter the default location for OneDrive. I selected the OneDrive directory I had created on the 2 terabyte drive and away it went. OneDrive did the math on the local drive disk space vs the space taken on the NAS via the symbolic links, concluded there was now sufficient for synchronisation and signed me in.
After a short while, OneDrive confirms the local data (on the NAS) is synced with the cloud and we are good to go.
Hope my experience is helpful to others.