The potential for ground loops is minimal since the common grounding points are located outside the panels, as long as the facility has a superior ground window.
The problem comes in how the grounds are commonized. Daisy chaining the ground from one panel using bare wires or two wires to a single lug is not acceptable by most national and/or operating-company standards. In the case of the latter, remember that lugs are not normally designed to handle more than one conductor.
Likewise, using two, single-wired lugs at the same ground terminal is also unacceptable. In this final case, — whether it’s a ground, signal or power terminal — the danger lies more in the disconnection of panels up-circuit of the terminal. Certainly one would notice that power goes off in the case of a separated power connection, but it is less obvious when dealing with a ground connection. Moreover, it’s a safety issue.