The documentation for SAML configuration for APM covers which UIs it does support (WebView, Web Start Workstation, and Command Center) but does not mention the Thick / StandAlone Workstation Client.
If SAML is enabled by setting the following property value in the IntroscopeEnterpriseManager.properties file
then the Enterprise manager will always redirect to the SAML Idp for authentication. So even if multiple realms are defined in the realms.xml file these will only be accessed for authorization after authentication has succeeded. Therefore when using the Thick workstation client authentication will fail as there is no Web UI involved for SAML to work with.
The Thick / Standalone Workstation Client cannot be used when SAML is enabled.