I would believe if your friend told you that bitcoin can be hack, but to hack the bets in gambling sites by just a calculator? I think that is impossible. There a lot of codes that is being generated by the code generator that changes the winning pattern on every gambling site, so the possibility that your friend that can hack the bets on bitcoin casinos are only 0.00000001 percent.
Why crack rate if you can have someone's purse and jam to follow them closely. This is easier. Though too difficult opportunities. Gambling on their own work so that the user personally gives the money voluntarily and forever.