Hi!
Did you install Mellanox ConnectX En driver on ESXi hosts?
You said CX-2 VPI interface not populates on ESXi 5.5U1.
There is some driver issue between ConnectX En and ConnectX VPI
There is difference in core component's version.
Therefore it's incapable load En and VPI interface together on same system now.
If you uninstall all the En driver then you'll be populating VPI interface with VPI driver install again.