I've been working on a vector field editor/importer/exporter off and on since I got UE4 and think it's stable enough to share at this point. It allows you to use particle simulations and vector math to influence the velocities at each point in the volume. The tool works on Bender versions 2.70 and up (untested on earlier versions).
There will be more features added over time, but there shouldn't be any major changes to the UI at this point.
Download here (Github)
I usually upload new changes to the 'testing' branch, but I think master and testing are currently identical.
Mostly finished documentation available here (Github wiki)
Example files (MediaFire):
Vector field in Blender
Vector field with velocities shown as 3D lines in blender (random noise):
The same vector field in UE4, used locally in a particle system with velocity-aligned sparks:
Feedback is very welcome. Have fun!