I think that MT4 and the ECN available through ForexPro are completely separate. It seems to be one or the other. I think ATCBrokers.com is just an IB for the different ECN platforms. The real test would be figuring out how they let MT4 go onto the ECN without running the MetaTrader4 API. I am considering signing up for a few demos of different types and then checking if the prices match. Of course, that won't count much and it will take a real money account to actually verify.

Lava FX allows automated trading through FIX API. That is exactly what I'm talking about implementing

CME.com is one of the biggest firms, but they don't have FIX and they don't deal with small players at all.