From the site description, it sounds like when you buy a "master" unit, you get a board that can control up to 2 additional "slave" spinners, and those spinners can be set ot be the Y or Z axis, by connecting them in certain ways.
That means the board probably looks like a single HID joystick, with x y and z axis, but they just report 0 values unless you hook up the slave spinners.
In that case, i'd doubt it would work to connect a trackball to it.
But shoot GGG an email to confirm. They're usually pretty good about responding.