Cannot Install SEP Client on workgroup computer

Hello -

I am working with SEPM 12.1 and cannot get the client installed on a Windows Server 2008 machine that is NOT currently on the domain. I am able to connect to the machine through the "Add Client" and can successfully start the installation but it fails every time. Is SEP able to install to workgrouped machines or do they need to belong to the domain? I can't think of a reason why they should but maybe I am overlooking something. Please advise. Thank you!