While I can't comment on ACM as I don't know them. Basically what real market makers do is called inventory management and market microstructure.

This means they try to keep an inventory of different currencies in their posession and align them to customer orders.

I think there are many fx market makers simply hold their customers positions and only hedge them on occassions. This exposes them to risk if customers positions are profitable as they will have to pay out the profits.

But this can get quite complicated as a market maker may also choose to hedge a certain % of orders or only hedge when customers have already "bought" all a currency in their inventory or when they are low on that currency in their inventory.

This is of course a very simplistic explanation, but what I am getting at is there are market makers who don't hedge properly and thus lose if customers make money, but there are probably others who do manage proper hedges (such as banks which are the biggest FX MM's), and thus worry more about inventory rather than individual positions.

I hope this answers some of your questions although this subject is immensly complex and each MM handles it in their own way... ECN's however, claim to pass the risk directly on to another participant (bank, MM, other traders) and thus claim to not trade against you...