Is 250mcm direct burial cable alum for 12 1000w mh lights.200a service

If its approved by UL it will have UL approved and a date on the lableing.

But that has nothing to do with how and where its used or what code allows in a situation.

First things first, how did you arrive at the 250 kcmil size cable?

Aluminum cable of the proper type insulation is approved for direct burial by the NEC. At 240 Vac you would only need 50Amps to supply 12000 Watts. That would fall out to be a Size #4 AWG cable.

At 120 Vac, the needed amperage would be 100 amps. Which falls out to be a 1/0 AWG conductor.

Now there are lots of other items to be concerned with such as the ambient temperature of your area. Adjustment and Correction factors based on the number of conductors and the heat generated by these un-grounded conductors. Voltage drop may or may not be a factor given the unknown distance (Voltage drop is only a recommendation by the NEC, it is not code enforceable).

Where is this installation going?

Maybe he got some of this wire for free?