In the context of gambling, random numbers or prngs can't have any unknown possible frequencies or tendencies. There can't be any doubt as to whether the number could be distorted or hallucinated. A pseudo random number that might or might not be from some algorithm picked by GPT is wayyyy worse than a mersenne twister, because it's open to distortion. Worse, there's no paper trail. MT is not the way to run a casino, or at least not sufficient, but at least you know it's pseudorandom based on a seed. With GPT you cannot know that, which means it doesn't fit the definition of "random" in any way. And if you find yourself watching a player getting blackjack 10 times in a row for $2k per bet, you will ask yourself where those numbers came from.
I think you're missing the point. Current incarnations of GPT can do tool calling, why shouldn't they be able to call on a CSPRNG if they think they'll need a genuinely random number?