The Dmax cooling system uses coolant to cool the entire block, heads, and EGR (applicable to all but 1st gen Dmax). The oil does not cool the bottom of the engine. The oil/coolant heat exchanger has two jobs:
1) warm the oil as quickly as possible to make sure oil is lubricating as well as possible
2) cool the oil to make sure it is not overheated
The goal is to have both the coolant and oil up to operating temp as soon as safely possible, and then have it stabilize. In essence, the oil temps are slave to the function of the coolant temps.
The Dmax with cooling system issues is the LLY second generation variation. The cooling issue is a result of the cooling system not being upsized when they added EGR when moving from 1st gen LB7 to 2nd gen LLY. The first gen LB7 didn't have EGR, so the cooling system was properly sized for that application. This is a point of consternation for many early LLY owners. (Late in the LLY sequence, they updated the cooling system and lead into the 3rd gen LBZ. The very late LLY engines don't have cooling problems. For more info, he'll have to seek out Dmax specific sites; too much to discuss here).
Generally, if his truck was not overheating the coolant, then it wasn't overheating the oil. If he saw 270 deg F on the oil, what were his coolant temps?
Now, I'll also say this about the temps he saw. Generally 270 deg seems hot to us, but it's not all that unique in the lube world for engine oil. Much of it depends upon where the temps are taken. But generally, that temp is not going to coke the oil immediately. It will probably hasten the oxidation of the oil. The only way to know the current condition of the oil is to get a UOA. The FP of oil is way above that 270 temp, so flash fire isn't an issue.