I don’t think it would be a very effective way of detecting money laundering (or attempting to do so).
It's not, but wager requirements have been justified before with similar ideas and rhetoric. KYC before deposit would work better, though not perfectly either - for every solution, there's probably a workaround.
A wagering requirement would probably do less to combat attempted money laundering than some kind of KYC requirement. The expected cost of attempting to use the casino as a means of laundering coin would be the wager requirement times the house edge (the higher your deposit is in relation to the minimum bet amount, the closer your actual cost to the expected cost will be).
A KYC requirement provided there is a sufficient chance the verification process will actually determine the identity of the person submitting the documents should prevent someone from attempting to launder coin.
Like I said, though, a little strange to deposit into a casino without the intention of betting.
In theory, someone could deposit a large amount with the intention of stopping to gamble if they have exceptionally bad or exceptionally good luck. I do agree that not gambling anything is not expected behavior of someone depositing at a casino.