CFDs = Bets. They are just pieces of paper that attempt to act as if you had a leveraged position in the asset. There is actually no asset changing hands.
Thus they don't directly (or even necessarily indirectly) affect the exchange rate. You could have 10,000 BTC bought or sold through CFDs and not one point of slippage on BTC would occur.
Also they don't even offer services to US citizens, and don't even offer metatrader software.
In other words, this should make little to no difference. I suppose it could get a few people knowing what BTC is. Other than that? nothing really.
You mean the site owners dont hedge against their losses?
That would in a small market like Bitcoin, that is so easy to manipulate with a couple million of USD be a fatal failure.
I guess they will hedge their risks on MtGox, thus buy/sell an equal amount of Bitcoins on MtGox that all their clients combined would costs them if they lost their bets against their customers.