I have this same question now.  Did you ever find a resolution to your question?

Uhm, those 2 connectors allow to use 2x U.2 enterprise units, or ( with a proper adapter to convert ), 2x M.2 units.

You cannot use them to drive sas units

I haven't setup that icy dock bay but I think it should work as the 2 ports are wired to the CPU and an installed Xeon will dedicates 8 lanes to them.  The icy dock backplane converts each lane to manage one SATA drive, so 8 SATA drives in that bay should work.

Forget about it..... ICY dock dosn't work with the PCIe lanes.

Maybe you didn't use the correct one

the plug on the mb is not a sff-8643 , but a sff-8639 . Same form factor, different signals and cable setup @Chino de Oro 

I have this one but it not works...      The miniSAS on 5820 MB seems only works with the panel below... which has a PLD chip and unique protocol on it...

As indicated before, I have not tried an Icy Dock with miniSAS HD connection.  Only making suggestion to check the connector types as they could be the reason for not working.

Beside, the Icy Docks will only fit properly in the 5.25" bay.  A comparison to OEM backplane for the flexbay is moot.  As time has progressed, pricing is also coming down.  Dell OEM backplane to use with miniSAS ports on motherboard became widely available.  It can be had for as low as $19 usd.  Who would want to get a pricy Icy alternative.