To any one that want to have the TFTP server included on OMV work together to Pi-hole, this are the guide:
1: first you need to download the pluging and configuere it properly:
And need a minimun config files: pxe.zip
then you need to configure pi-hole to use external TFTP server.
to do this only need to create a new file on /etc/dnsmasq.d/ named : 10-TFTP.conf <-/etc/dnsmasq.d/ is where you configure pihole to store persistent data
and add this lines:
where 192.168.1.4 is the IP of your NAS ( the IP when TFTP server is running).
and restart the DHCH server of pi-hole ( you can do it from webGUI):
and test that all works.
finally a screen capture of my pi-hole config and some usefull links:
full pxe enviroment for backup pourpouses: MEGA