The Workflow Server portion of Workflow is the only thing delivered on the SMP when Workflow Solution is installed. Workflow Designer/Process Manager are not installed. Workflow Server is installed such that SMP can host the Publishing Controller workflow delivered by the Workflow solution.
There's nothing stopping you from installing Workflow Designer or Process Manager on your SMP. You can run the installer that's stored at Program Files/Altiris/Workflow/Web/Agent and install them on the SMP. However, since the SMP is somewhat resource-intensive, it's probably a good idea to keep them off box.