They will need a copy of RailClone Pro to render the scene, but we can send a NFR license to them.
About the installation, the registry keys are required only for the interactive mode. The plugin can be installed in the render nodes copying only some files. The procedure is describe here (see the Network rendering section):http://www.itoosoft.com/railclone/reference/reftechnical.php
Please, give me a contact e-mail and i will write to Andre.
Alternatively, you would convert RailClone to stand-alone objects, using the new instancing tool included in v.1.3.0 (RailClone Tools). Once converted, you can remove the RailClone objects from the scene, so it is not needed to have the plugin in the render farm.