From my understanding, network discovery happens mainly at layer 2 so your MAAS box would need to be setup on each vlan in your datacenter. This will also simplify your DHCP setup since you won’t have to mess with DHCP relays or trying to route DHCP packets. In our setup, I made the interface on the switch that our maas box is connected to a trunk port so it has access to all vlans. (This could be restricted to only the necessary vlans if you want.) Then, I added the vlans to the interface of my MAAS box.
This may also help with the issue you were having in your other post.
https://discourse.maas.io/t/commissioning-failure/6507