Bitcoins can be used to deposit at online casinos and take out bitcoins. This is something that will be more of in the future. At NETeller, an international bank, were you can get a physical and online prepaid visa, they offer deposits with bitcoins. With todays many deposit options and withdrawals bitcoin can be used not only as direct payment but also indirect. Remember that many casinos withdraw your money with the same method you have deposited.
Now almost all casinos offer bitcoins as payment and witthdrawal option. See below casinos allowing bitcoins as deposit methods.
Club World Casino
Captain Jack Casino
Wild Vegas Casino
Planet 7 Casino
Depositing money at online casino and sportsbooks is generally safe, but to be on the more safe side, check out eCOGRA that has a list of accepted casinos, made for the safety for the online player. Just to be extra sure.