There's no good way to know if a transaction will ever make it onto the blockchain.  Even if you see it in a block it's possible that block will end up orphaned, and the transaction could end up being invalidated by the block which replaces it.

So if you want to be able to pay out winners without waiting for a bunch of confirmations, you're sometimes going to be at risk of paying out using transactions which will never confirm.  Unless you have a big enough hot wallet that you always have some old coins sitting in reserve to pay people out with.

When you have the kind of volume that SD has, I guess the coins in your hot wallet don't have a chance to get very old.