It took me a LOT of time to compile the right set of plugins needed for Eclipse RCP Help. I could find few related articles but they were outdated for Ganymede. First of all there is no need for any compile time dependency to be added to your plugin.xml. If you have a basic RCP application, which has no help in it, you need to add these plugins to enable Help on top of the plugins which you already have. They only need to be in the target platform. Below are the plugins which you need to have in your target platform. Make sure to add them to your product as well.
Note: You no longer need org.eclipse.help.appserver and org.eclipse.tomcat plugins in your target platform in 3.4 (Ganymede).