I cannot speak for Granite devices, but generally the term Frame Ground FG refers to the part of the device that comes in contact with the outer metallic case etc that would contact the enclosure or Service grounded point when mounted.
Other connections are named chassis ground, Logic Ground, Power common, and these may be isolated from the case or Frame ground, then it can be made optional as to whether these are tied to the FG.
There are basically two schools of thought or practices as to whether all systems are kept isolated from each other or tied together and connected to a common ground and machine bonding point.
Personnaly, I find it misleading and bad practice to call these other commons 'ground' when in fact they may not be at all at ground potential, and misleading, especially to those who are newcomers to electronics.
The bottom line is, you should only have one ground point set up that bonds the service ground to all the metalic points on the machine, together with the rest of your grounded commons and shields.