@awines
This question would be best places with Workday, as they built and maintain the integration with Docusign eSignature. I am not aware if Workday has a feature roadmap at all and if this will be part in the future. It’s probably not a big change to the existing integration, but needs to be developed, tested and released.
As a workaround with most integrations that have only implemented limited functionality for Docusign eSignature, a potential workaround may be to leverage a template and add the witness there. It may not be automatically pre-filled by the Workday integration, but ideally you will have the option to manually add the witness details when sending the envelope from Workday.