I am not that familiar with FMESererJobSubmitter but I believe you might need to write the output in a folder on Server and then retrieve those results.I didn't took this approach as I thought it was going to affect the overall time of this workspace to run as I am trying to optimise it as much as possible.If you have experience using it, would you say it is worth trying it?
Is there a reason you are using the httpCaller instead of the FMEServerJobSubmitter?