In an interview with Gamespot UK developer of Splinter Cell 3D said
"FC: The 3DS is powerful, and we are able to run the Unreal engine on this console, which is pretty impressive for a handheld machine, and the 3D doesn't affect the performance (thanks to my amazing programmers). The architecture is different compared to a Wii or some other platforms that we had to work with here at Ubisoft Montreal."
So when it was told that the Unreal Engine can't be run on the 3DS, that was BS look at this. Just Epic being lazy, really dissapointing, but I guess it's there choice.