"[...] or perhaps due to a theory that my true identity was an immortal gambler." (jack the ripper, fate strange fake vol 6)

with that said, jack has knowledge on gambling. even though one of flat escardos' skills is cheating to a memetic degree, jack will do their best to play clean. they're only going to play what they know, which is roulette and poker/blackjack, betting modestly. they have good self-control and know when to pull away.