I have connected a Dawicontrol DC-6510 PM (Sil3726 chipset) to the SATA port of a D54250WYK NUC. I have updated the D54250WYK its BIOS version from factory 0018 to 0022. I connected two 2.5" drives to the port multiplier and the port multiplier to the NUC.
The result is that the drives behind the port multiplier could not be detected by a 64-bit Windows 8.1 Pro OS, in other words Intel Haswell NUC's do not support SATA port multiplier technology. After removing the port multiplier, and connecting that drive directly to the motherboard SATA connector, the drive was correctly identified by the Windows OS.
Note #1: attaching only 1 drive succeeds
When attaching only 1 drive to the port multiplier allows the Haswell NUC to boot from it. But attaching only 1 drive defeats the purpose of a port multiplies, which is connecting multiple drives to one SATA port.
Update #2: tested with Ubuntu 13.10 Linux
I have repeated this test by connecting two 3.5" drives behind the same Dawicontrol DC-6510 PM and attaching that port multiplier to the blue SATA of the D54250WYK. Neither the BIOS of the NUC nor the Ubuntu 13.10 amd64 installer is able to detect any of the two drives that are connected to the port multiplier.
This leads to the conclusion that the Intel Haswell NUC built in SATA port does not support port multiplier technology.