CA Product management has not tested UnboundID as a Policy Store for CA Single Sign On (Siteminder).
However, UnboundID, as part of the CA partner program has independently tested their solution themselves.
Please reach out to UnboundID to understand which versions and platforms they have certified to work with CA SIngle Sign On for your particular needs.
You can reach UnboundID support here: Support & Training | Enhance Customer Experience | UnboundID