I also managed to get this working with THECUS NAS. It is tested on N4200PRO (pending test on N5500). I think it will work on most of the recent Thecus NAS (same firmware file).
Brief Installation instructions:
1. Upgrade to the NAS to the latest firmware (current V5.02.02).
2. Install from this site http://www.fajo.de/main/en/thecus/modules
(thank you John Falk for those modules) the following modules with this order:
a. ModBase1 (http://www.fajo.de/main/en/thecus/modules/modbase1
b. Perl514 (http://www.fajo.de/main/en/thecus/modules/perl514
c. FaJoSSHD (http://www.fajo.de/main/en/thecus/modules/fajosshd
3. Configure FajoSSHD listening port to 22
4. ssh to thecus with username root and Password (your admin password). Type "cd /sbin" ; " ln -s /raid/data/module/Perl514/system/bin/perl";
5. Enable NFS on thecus and allow NFS access from the IPs of ESXi servers and B&R Servers.
6. Proceed with the usual Linux repository target installation from Veeam B&R console.
The performance seems good (48MB/s).
Hope this mini guide will help.