no way to know without testing. for instance,
if you have no control over the firewall, then might be limited to very slow DERP relay servers.
- cannot open port
41641 - NAT-PMP might not work
i do a similar thing, run veeam, backup replication server, backup repositories, and agents over tailscale.
i also have a few synology boxes, running tailscale.
all work great.
the problem with webdav, in most cases, cannot verify file transfers using checksums.
fwiw, using tailscale, i prefer smb/samba. most any backup software can work with that.
check out my howto - How to access SMB/SAMBA with rclone