I can't speak directly to that particular BOB as I have never used it, but it is my custom with PC system installations is to make all power supplies common to a Earth ground star point.
I have just used opto's to transition from one power level to another, but either side is ground common.
Although the the PC MB/P.S. is at ground potential via the power cord, I also ensure a bonding conductor from the PC chassis frame to the star point.
So far this method has served well.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.