They can be exported with a bit of playing around, 
Create a duplicate character in a new folder for testing.
In the mesh panel at the top bake out the textures to a 4096x4096 size,
this will create your defuse textures,
then create new materials based off the normal original textures with the normal plugged into defuse slot,
remove all the other materials and replace the new normal materials in the body legs and head slots,
do a second bake as above, now you have defuse and normal textures,
I assume this is all ok so long as they end up back in UE as part of a cooked project, and not distributed independently.
If someone official could clarify it would be greatly appreciated.