What are you asking about here? Like who initiated the document? (that's part of the workflowContext that's available to your script code). Or is it who did what with an asset going through the workflow? Are you talking about the separate workflow plugins and how they deal w/ assets?
There's no real "userids of users" passed through a workflow. A workflow applied to users gets invoked on each user, not a group. And only a single user can do something to start a workflow on an asset, so there's no real users.
