That is correct and at the same time the very difficult part. ;)
They usually send back the originally deposited to where it came from, only the above balance may be cashed out in a method picked by you.

One casino I did find was wildjack.de (also exists with a .com domain, I believe). Unfortunately when I tried it with a small amount of 100 EUR I did not see the fee attached to a wire transfer below 1000 EUR, thus my little experiment cost me 25 EUR. ;)
Right now they somehow don't accept my CC anymore - don't know if that is on part of the casino or on part of my bank, I may try to figure that when I get home (don't really wanna mess with casinos while in the US).

Let's assume your statement prints on the first of every month. If U buy a $5000 air ticket in March, the CC will send your miles/points over on April 1. If U then refund it in April & also spend $5000 on your card in April, you will get 0 miles on May 1. If U spend <$5K, I assume U would get negative miles on May 1. If that withdrawal of miles puts your FF acct. below zero, U may be in trouble. It depends on whether the airline or hotel co. trusts U to earn to bring your balance up to zero.

Moral: I would consider doing it as a way of borrowing/ being advanced miles which I need earlier than I would really earn 'em, but not as a way of scamming for miles permanently.

Several years ago, you used to be able to get cash advances from cruise ship casinos, and they would charge it to your room like anything else you'd buy on board - at the end, you just leave your whole bill on your credit card (I started a thread on this called "Miles on Royal Caribbean,", but I think it's too old to pull up). I think most cruise lines have closed this loophole since then.