Real-life gambling laws prohibit GTA Online players in certain countries from gambling in The Diamond Casino & Resort.

This is due to your country/government and the laws they have in place for Gambling.

The Martingale system is perfectly legal. Many online casino players use it to determine how much to stake on each hand or spin of the wheel. You can also use the Martingale system in sports betting., but a horse racing Martingale system would be difficult.

No, but there's no reason they would ever kick anyone out for that. Far more likely, the player would get a comp of some kind to encourage them to play longer.