I should point out that we also have a FreeBSD box running FreeNAS with a Chelsio 40GbE card in it. That's connected to the switch via the 2m Tripp-lite cable mentioned above, and is working perfectly with no configuration needed on the switch side. It was auto-detected an the link is active. I tried that same cable with the Mellanox cards and it's not working.
The issue seems to be with either the Mellanox cards and this switch, or with the cables, maybe?
This may be caused by old firmware on the ConnectX-3 adapter.
The firmware should be at least 2.32.5550 for ConnectX-3 adapters.
I recommend updating the adapter fw to the latest version which has improved compatibility.
You can see the current firmware version using the vstat command.
The WinOF driver supports the 64 bit version of Windows 7 only (not 32 bit) with no virtualization ( no SR-IOV).
Also, if the switch is running older software that could prevent it from linking with certain adapters/switches.