Any operator or operator group that has the named right WORKFLOW is able to start or stop a workflow.
workflow supervisor group is operators that are notified if a workflow failed and they may not have workflow right
I see that named Workflow rights may be assigned to any group to start a workflow.
For the standard groups, does the delivery operator group has the right to start it?
According to user rights matrix, Campaign managers also have named WORKFLOW rights .
As mentioned above by David, For this just go to
a) Admin->Operator Group
select required operator group and click on Content Tab and check for Workflow Named rights