Hey
I do this a lot, though not with deadline, I've used tractor and royal render, but should be no different.
Just enable the write to GI cache file, and set the directory in terragen for the cache, and it will only produce the cache, not the full image.
I usually only render the GI for every third frame, (most render managers should give you the option) and use the interpolation when rendering the final output.
Hope that helps
Chris