Greetings, OMVers:
I created the following script to re-mount all the inactive sharedfolder mounts in one go and just created an @boot scheduled job to run it. Working fine for me so far after each reboot. However it's still safer to have all processes to use the actual mounts located under /srv than the /sharedfoldes reference ones.
Bash: remount-sharedfolders.sh
#!/bin/bash
for FOLDER in `systemctl list-units --state=inactive -t mount | grep sharedfolders | awk '{print $1}'`
do systemctl restart $FOLDER
done
Hope this helps!
P.S. Just want to point out that this solution will work for people who's been setting up multiple mergerfs sharedfolders (like me) and you don't need to mess with multiple auto-generated systemd service/mount files. However the re-mounting does come slightly delayed during the boot process, compared to solutions suggested before.