Without knowing his inverter size, we can't tell if there is an issue, but probably not.
His wiring looks like this:
Spreading it out, this is essentially the same.
Notice that each segment between batteries carries a different fraction of the total. Since the segments are 2/0, the total current it can carry is 285 Amps (I am using the ABYC standard since it is mobile) . 3/4 of 380A is 285A so as long as the total load is less than 380A it should be OK.
The interesting thing is that the ABYC rating for 4/0 is 385A, so as long as he sized the 4/0 correctly he is probably OK.