Hi Santosh,
Yes, it is possible via the "SAML proxy" scenario if Siteminder supports this scenario. Maybe you remember that we discussed with you this sceario last year via the e-mail. You have to make sure that the implementation is following the IDP initiated configuration. SAP SAML IDP will have to call the SP side of the non-SAP solution (Siteminder) and then the IDP side of the non-SAP solution (Siteminder) will have to call Fiori (AS ABAP SP).
Regards,
Donka Dimitrova