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
Please note that while this was correct data at the time, It is no longer correct. Now that UnboundID has been acquired, the relationship between CA and UnboundID has changed. Please refer to the bottom of the PSM page on the support site for an authoritative list of validated partners. CA SiteMinder Informational Documentation Index - CA Technologies
it is important to also mention that validation of a third party integration is different than CA saying it supported by CA.