I created a VLAN and a QEMU bridged network, both work fine but when I create a VM in the KVM pod, DHCP is not giving any address and is not pxe-booting.
If you are turning DHCP on a bridge interface created by virsh (aka. virbrX) then you need to be sure that you have the DHCP server turned off on that network defined in virsh.
If you do not do this then virsh will run its own DHCP server instead of MAAS and MAAS will not be able to provide the DHCP addresses or the next-server DHCP options for the VM to PXE boot.
Try disabling STP on the vmnw0 interface. I have seen issues where STP causes the virtual bridge to not work with DHCP, mainly when the DHCP server is on the same host that has the bridge.