They'll need the entire WebHelp folder from your project's \!SSL!\ folder and possibly the CSH_API programs found on your RH install folder.
Helpful and Handy Links
Adding to Jeff's comments, here are some key links to "all things context sensitive" that might be helpful.
The APIs themselves can be found on your author hard drive under this path (or where your RoboHelp was installed)
C:\Program Files (x86)\Adobe\Adobe RoboHelp 9\CSH API
Depending on the CSH technique that is used, your developer will need one of these API files to include in their project.
Peter Grainge has a very nice wrapup of many ways to call WebHelp and you will find them here:
Willam Van Weelden has made a nice contribution that includes a CSH tester.
Finally, I wrote an article for Adobe Dev Net which is a little old, but the principles have not changed at all and some find this helpful
Adobe Certified RoboHelp and Captivate Instructor