Everyone I have made this easier for you.
If you are running a MAC PRO 6,1 Late 2013 Model or newer (i just got mine new from apple 12/2015)
Please use the link I will provide in this markup.
This does have the ESXiBase of: VMware-VMvisor-Installer-6.0.0.update01-3073146.x86_64.iso
The Driver was obtained here: https://vibsdepot.v-front.de/wiki/index.php/Sata-xahci
With the following Community Supporte SATA - xAHCI Drivers that allow the ESXi 6 install process to locate and install to the Newer SSD drive in your MAC Pro.
***Also the file name is ID's as ESXi 5 (ignore this It is actuall ESXi 6)
This is posted AS-IS, and is again community sponsored.
I used the Package Identified in this post to inject the drivers and create the bootabler ISO image.
Simply download and burn to CD, then install away.
I will keep the ISO on my google Drive for a time, but will eventually remove it so this link may go dark after some time.
Link is here.