Is there a way to classify DHCP requests based on the interface they're coming from?
When a router or other device relays a DHCP request, it sends along with it the subnet information of the interface that it received the request on. In other words, the point of relay is that your DHCP server does not need an interface on each VLAN to serve multiple subnets.
Are you trying to override that behavior and issue an IP address in a different subnet then is on the interface?
Maybe someone can clarify, but I believe if you have it listening on all those interfaces, it will issue an IP from the subnet which is configured on that interface.