If the tray meets the cross section requirement in table 392.60(A), you agree that this is "where continuous maintenance and supervision" and they tray is connected to the equipment at both ends with a 3/0, it is legal.
I agree supplemental grounding is just that, more than you require.
The handbook warns about assemblies of conductors may have insufficient grounding conductors when used as parallel sets.
Cable assemblies are manufactured in standard conductor size configurations, and the equipment grounding conductor in a cable is properly sized for some circuit arrangements but not necessarily for all parallel circuit arrangements. Where the cable is used in large-capacity parallel circuits, it is necessary to ensure that the equipment grounding conductor in each cable is sized as required by Table 250.122, based on the size of the overcurrent device protecting the circuit.
Each parallel set (in a raceway) shall be 250.122.
The cable tray gives you more latitude the way I read it.