You cant use the DOM to enter FX spot orders, they have got a seperate order interface for that (without a dom-ladder). Its called FxPro or something.
You can trade HotspotFXr through Mirus with Ninjatrader/Zenfire, but its expensive ($5 per 100K traded).
Ninja can also connect to MBTrading and IB for FX trading. IB provides the most bang for the buck, the other options are too expensive in my opinion.