I can only speak for bustadice, which does indeed use 2-of-3 multisig wallet, of which I hold one of those 3 keys.  I can independently verify bustadice's player profit/loss (and thus investor profit/loss). So I use that to guide if I should sign a transaction. Although worth emphasizing that  independently verifying player profit/loss is not really enough information to do a great job at being a cold-wallet-key-holder because I have no way to independently verify the bankroll size. (i.e. If Daniel was malicious, he could simply say "Oh we've had a mass exodus of investors. Need you to sign the withdrawal so I have enough funds to pay them" and I'd have no way to know either way).

I have a special role for bustadice (I run the audit server, and hold one of the keys). But don't provide a similar service for bustabit. I could however take a pretty good guess at what Daniel is doing for cold storage there, but it's not really my place to do so.