I think with CFD you only allow trades between two users. The house never takes a position. When the contract ends or a margin call occurs the loser's margin is transferred to the winner.
In theory yes. However there have been cases of less than ethical houses front-running against their own clients. Think about it - they know about the price changes before their exchange platform uses it. (because they just get the exchange rate from MtGox like everyone else).
On the flip side if they do run a ethical exchange, why not write your own bot, and set it up on a server in Japan. You'll get the price change information first and can potentially outsmart your competition on their exchange.