So here a shitty diagram of my network:
network diagram

I want both subnets to be able to use the openwrt router as pxe boot server.
I can't change the dhcp config on the fritzbox though so normally you would enrich it with this:

dhcp-range=10.0.0.0,proxy
dhcp-boot=pxelinux.0,10.0.0.3,10.0.0.0
pxe-service=x86PC,"Automatic Network boot",pxelinux
enable-tftp
tftp-root=/usr/tftproot

can the openwrt router also does this with ?
what would I need to add to the /etc/config/dhcp file?