To anyone coming across this, as of July 2015 helpshift almost certainly will not work on Phonegap build in its current state.
The reason for this is they are not setting up the SDK correctly with the plugin. As with all cordova/phonegap plugins, the necessary files to make the integration happen need to be copied over in the plugin instructions, however, as per the helpshift docs there are a lot of manual steps that need to be taken in xCode to make the integration take.
I have seen an open source project try and fix this, however building didn't work for me in that either.
The solution right now is as follows: (for iOS)
Use Cordova (yes this means that you can stop reading if you have to use PG build)
Add iOS to your project
Install the Helpshift phonegap plugin using
cordova plugin add <path to helpshift plugin>
Once complete, jump on over to
https://developers.helpshift.com/ios/getting-started/#automated-integration
and download the helpshift automated integration assistant.
Run through it, installing v4.9.1 (later ones have issues with resources missing)
Jump on in to xCode and run your project, it should build just fine... Now follow the instructions on initialising helpshift in phonegap
https://developers.helpshift.com/phonegap/?_ga=1.99559902.1744288086.1387515146#initializing-helpshift-phonegap-plugin
*** Another point to note, their plugin is single platform only. I have made a copy of it that is doing both Android and iOS but have not yet worked out how to get android to fire with a recent version of Cordova Android. The gradle integration isn't compiling and the guide on their site cant find the SDK. I'll post a link to the multi platform version of the plugin once its all working.