The management IP can be the loopback IP. Any IP address assigned to a switch can be a management IP as you can telnet to the switch on any available IP.
Often, a management Vlan is created in multi-layer switches so you can single-out traffic to/from the switch for management purposes.
On a Layer2 switch, you are only allowed to have one Layer3 address and that's the management IP.
As for the loopback, it's often created since the interface is always up/up. The management IP under the switch virtual interface, relies on the port status to be active in order for the interface to be up/up.
For instance, if you have a management Vlan of 100, you need to have a switchport in up/up state with trunking enabled and Vlan100 in forwarding mode -or- a switchport configured as access-mode for Vlan100 and status up/up.
HTH,
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Edison.
