SD.IncidentManagement as the workflow package name under ServiceDesk 7.1. 7.5 uses the name SD.IncidentManagementSimple, so that's why your name convention is different.
As for the service itself, if you take off the "?WSDL" from your URL and navigate to it in a web browser, preferebly on the ServiceDesk server itself, you'll see the main workflow service page. Clicking on one of the operations will display the XML that the operation needs. If you are on the server doing this, you should also get an invoke button that will take you to a page that helps identify what data is needed for each operation. I'm guessing this will point you to what data you need to pass.
That said, why not just make another workflow project that uses the existing "Submit Incident" component? Or, if you feel like playing with some rules and maybe modifying the monitor project, just have emails sent to ServiceDesk that create the incidents for you?