Most game engines usually have a converter of some kind so you can use AC3D, export some format, say Collade .dae, and then convert it for the engine.
A quick Google for this engine found
https://github.com/returnString/CryEngine.RC
I have no experience of this but it looks like you can convert Collada files to this engine's format. There are probably other converters too.
This applies to many engines and other software. Just because someone has implemented a native export for blender, doesn't mean it's the best way to make geometry
