Both the AP Manger interface and the management interface can be on the same subnet. The important thing is that the management interface and the AP Manager interface have to be reachable from the LAPs. It is usually configured on the same VLAN or IP subnet as the management interface, but this is not a requirement.
when you have multiple AP Manager interfaces configured to support a maximum number of LAPs, all the AP Manager interfaces have to be on the same subnet. You need Layer 3 connectivity between LAPs and the AP Manager and management interfaces on the Wireless LAN Controller (WLC). The LAPs can still be configured to be on different subnets.