No, the CA API Developer Portal is not vulnerable to CVE-2017-9805 as Apache Struts is not used in the product. In fact, Apache Stuts is not used in the API Gateway or related products either, meaning that none of the CA API Management products are vulnerable to any Apache Struts-related CVE. Note: This may be subject to change in the future, but as of the time of this writing, no CA API Management products are actively including Apache Struts.
Additionally, Red Hat states the following on their page for CVE-2017-9805:
"This issue did not affect any of the Red Hat products as they did not include the Apache Struts 2 package."