First off, the MHGH28/29 only work with 2.7 and ESXi. They won't show up with anything newer. I think that the ConnectX is stuck at that firmware for VMware... Mellanox has to plans to fix it.
Secondly, check your cables. Some of the cables sold on ebay are only rated for 10Gbps. Not sure if they are printed anywhere on there though. You could just plug two cables in direct, and see if they can link at 4xDDR.
I'll try to think of other things as well, but it was literally plug and play for me.
Here is the result of my ibnetdiscover:
Switch 24 "S-0008f104004128f4" # "ISR9024D Voltaire" base port 0 lid 2 lmc 0
[1] "H-0002c903000284b4"[1](2c903000284b5) # "basement mlx4_0" lid 4 4xDDR
[3] "H-0002c9030000fe6c"[1](2c9030000fe6d) # "xxx.xxx.xxx.comcast.net HCA-1" lid 6 4xDDR
[5] "H-0002c90300015230"[1](2c90300015231) # "esx2 mlx4_0" lid 3 4xDDR
[7] "H-0002c9030000ffac"[1](2c9030000ffad) # "node0 mlx4_0" lid 5 4xDDR
Likewise: iblinkinfo:
CA: node0 mlx4_0:
0x0002c9030000ffad 5 1[ ] ==( 4X 5.0 Gbps Active/ LinkUp)==> 2 7[ ] "ISR9024D Voltaire" ( )
CA: esx2 mlx4_0:
0x0002c90300015231 3 1[ ] ==( 4X 5.0 Gbps Active/ LinkUp)==> 2 5[ ] "ISR9024D Voltaire" ( )
CA: xxx.xxx.xxx.comcast.net HCA-1:
0x0002c9030000fe6d 6 1[ ] ==( 4X 5.0 Gbps Active/ LinkUp)==> 2 3[ ] "ISR9024D Voltaire" ( )
Switch: 0x0008f104004128f4 ISR9024D Voltaire:
2 1[ ] ==( 4X 5.0 Gbps Active/ LinkUp)==> 4 1[ ] "basement mlx4_0" ( )
2 2[ ] ==( Down/ Polling)==> [ ] "" ( )
2 3[ ] ==( 4X 5.0 Gbps Active/ LinkUp)==> 6 1[ ] "xxx.xxx.xxx.comcast.net HCA-1" ( )
2 4[ ] ==( Down/ Polling)==> [ ] "" ( )
2 5[ ] ==( 4X 5.0 Gbps Active/ LinkUp)==> 3 1[ ] "esx2 mlx4_0" ( )
2 6[ ] ==( Down/ Polling)==> [ ] "" ( )
2 7[ ] ==( 4X 5.0 Gbps Active/ LinkUp)==> 5 1[ ] "node0 mlx4_0" ( )