Assume a 400A service consisting of 2 - 200A main circuit breaker panelboards. From the service point to the meter socket, parallel 2/0 AWG conductors are used for the ungrounded conductors. On the load side of the meter socket, single 3/0 AWG conductors are installed to each 200A panelboard. The total calculated load is 250A.

Does this arrangement meet all the requirements of the NEC - (230.90, 310.15)?

The paralleled 2/0 AWG conductors will not be loaded to greater than 250A and have a derated ampacity of 280A. This complies with Exception #3 to 230.90(A). However, the individual service entrance conductors to each 200A panelboard must comply with the 310.16 rating of 200A or 3/0 AWG...

(The occupancy is NOT a dwelling)

I would think it does comply, but I would want to know the length of the runs to each panel and if the mains are grouped.

Bryan, I assume that the parallel conductors are installed in the same raceway to require the ampacity to be derated 80%.

You are 100% correct.