In fact, these are highly recommended due to the low cost and speed of the transactions. All casinos operate on the account system - you send them money and your account is credited for that amount. As you gamble, money is credited or debited as you win or lose. Many operations now allow you to have money withdrawn directly placed back onto the credit card that you first deposited money into your account with. This option is recommended as you can access your winnings within days.
Casinos charge reasonable fees for other withdrawal options.
How safe is anything. So far there have been almost no problems with casino payouts and deposit security, but that is not to say there will never be. Many of the jurisdictions require that the licensee posts bonds of cash or insurance as part of the license requirements. As an example, the groups licensed in Curacao have to post an amount of money equal to the average win in a special account in order to guarantee that they can pay winners. To even get a license, those who apply have to go through some extensive government checks.