NBA indeed has cash considerations during trades. And yes, the amount is related to the salary cap (of course). How it works is that each team has a set dollar amount of cash that they can use in trades. They can use all of them in 1 trade, or split it in multiple trades. I think we are all aware of the salary matching rule that the NBA implements in trades, right? Well the cash consideration cannot be included in the computation of that salary matching. Cash consideration is just used as plain old sweetener in trades. But given the limited amount of, it rarely provides any actual sweetness.
I think you are just assuming that, unless you can provide any actual report that this is not included in the official record. Given that the lopsided trades (with significant cash amounts included) were approved by the PBA's committee, i am inclined to believe that the cash considerations were, indeed, considered during deliberation and therefore were recorded.