Usually when there is a 0 confirmation policy in terms of gambling, the payment back is sent using the funds of the money sent in, so if that never confirms, your payment back will also never confirm (correct me if I'm wrong). Luckyb.it has 0 confirmations, and they pay back within roughly 10 seconds from your bet (technically instant if you don't count the plinko animation), so theres an example. I think there is a way to purposefully make it so it doesn't confirm, so I don't know how that would work on luckyb.it
That would not work with LB for sure because even though you can double-spend with 10(max) sec interval LB still delays payments that are at risk
plus even if you manage to double-spend after 10 sec they still spend your unconfirmed inputs as payout so your double-spend has lover chance of winning the race.