I have a 2 node netrender setup that is fully functional with Blender render engine but not Cycles. When I do this it is rendering because it takes some time for it to return the blank images but it is not rendering the animation. If you need more information just ask nicely please :)
I don't know how to fix your problem with netrender, but a possible alternative method you could use is to tell each server to write to a shared directory, enable Placeholders and disable Overwrite.
With Overwrite disabled, each server will check to see if a file already exists where it would otherwise write the next frame. If it does, it checks the next frame, and the next, and the next, until it finds a frame where no file exists. Then it will render that frame and write it.
Enabling Placeholders makes the server write a "dummy" file when it starts rendering to "reserve" that filename for the render when is complete. This ensures that one server doesn't start rendering the same frame another server is already rendering but hasn't written yet.
I had this problem using blender 2.69 on Ubuntu. I downgraded my net render nodes to the version in the Ubuntu repositories (2.66a) and the problem went away. Never could get it working in 2.69. In my console output, 2.69 wrote .png files, and then complained that it couldn't find the .exr files.