Yes, there are better ways for doing this. You definitely want to avoid a workflow which copies anything to the vRA/vRO appliances. If you can give more details about what you're trying to accomplish, we can suggest alternatives.
A tool creates an XML file which then must be read and processed by a vRO workflow. Of course there is also the option that the tool makes a api call with the XML string as content. But the customer wanted an XML file to be generated, which can also be archived.
I would handle this by publishing that XML file to a very simple web server and then having vRO do a call to that URI to get the contents of the XML.
Can you place the file on shared storage like a netapp or something that both the windows system and the vRO appliance can speak to? Or can you run the process twice the first time dropping a file somewhere and the second time making a call directly to orchestrator with the xml as the payload? If you can only do a single run of this tool you could call orchestrator, process the xml, and then drop a file or email the xml somewhere.
We also have windows hosts we use as helpers in our environment so maybe you could do your processing within one of those helpers? We make calls via the guest tools and extract the results from the output of powershell or other command line tools.