Do you have anything more than an ad hominem attack to offer?
A request for evidence for assertions is not an ad hominem attack.
However, I will say that the two institutions mentioned are primary broker-dealers. They own the casino, and get a cut of every bet their customers place. It’s a highly profitable business, and they have no need to place bets themselves.
The other argument is that internet rumor-mongers have been alleging this for years. If their allegations were true, huge losses would have showed up in the quarterly reporting by now, since commodity contracts are usually less than a year in duration. Since no such losses have been reported, it is safe to say that the rumors are likely to be wrong.