Hi Stuart,
I hope you are doing well.
The Fusion team is working on an app connector for Workday, it's expected for release this summer. That said, some Fusion users are already using Workday in their Fusion scenarios using Workday's Reporting as a Service capability.
This article describes how to use Workday's RaaS to get data from Workday. I suggest taking a look to see if it will meet your needs.