To make sure it is Irradiance causing the problem, switch to Brute Force and see if you get similar results. If it doesn't do it in Brute Force, you could either stick with that (I stopped using Irradiance for the vast majority of scenes, BF has come a long way in terms of speed), or try first rendering out and saving the Irradiance to a location they can all access, then render the final using DR. It should transfer during DR though, but redundancy doesn't hurt.
Also make sure that any textures/maps are accessible to the nodes, and/or turn on Transfer Missing Assets in the distributed rendering settings dialog if it isn't on already.
I have also had issues with a couple DR nodes that would not honor the gamma settings assigned to textures/environments, and would return back wrong results. The render element VRayDRBucket can help diagnose if it is only certain nodes causing the issue, or all of them.
I wouldn't use progressive, that isn't solving the problem as to why the DR nodes aren't receiving the proper information, but is hiding it by mixing in their bad results with good results. So if you render a patch, it might not match up to the rest of the render. It can also be slower and takes up more RAM if you need to render a larger image.
And like all posts involving other render engines, I suggest visiting the Chaos Group forums. You'll get much more valid information there. Almost all of my VRay issues were solved there.
