From the VBII manual:

"The Vagabond II system includes a Ground Fault Circuit Interrupter (GFCI). A GFCI is an electrical device that monitors the electricity flowing in a circuit to detect ground faults. This built-in GFCI allows for safe operation of the system without the physical ground requirement."

The unit indeed has a port labeled "GND" on it, and ships with a wire to physically ground the unit. However, according to the manual, the explanation of the Ground Outlet states:

"A ground outlet is included but is no longer necessary, as the VII's PSI900GF inverter incorporates a built-in ground fault interrupter and does not need to be physically grounded for safe operation."

Long story short, the unit won't ship with the ground cord, and as noted in the manual, it's not necessary. I've been running two of these in the field and have never manually grounded a unit--and I've never had an issue.

VBII Manual