Greetings!
For OoBM-MAD to function properly, the active management module (MM) for each member must be able to connect to the active MM on the other member regardless of which MM is active on either chassis. Keeping that in mind, you would need to connect both OoBM ports on both members to a common switch rather than directly connecting the MMs to each other. This way, either MM will be able to communicate with its active counterpart, even in the event of a MM failure on either chassis.
Note that only one OoBM port on each VSF member will actually be up at any given time, as the inactive MM in a VSF-enabled 5400R chassis is automatically shutdown when it is inserted or detected during the boot process.