If the integration between ACS 5.6 and Cloud based radius / AD has been done then the next step is to :
1. Active Directory > Directory Groups > Select the AD groups you want to use for in your authorization conditions.
2. create an identity source sequence with Cloud based radius server selected inside the authentication section and AD inside additional attribute retrieval say RSA-AD
3. While creating the authorization rule in access-policies use External AD group in condition to accomplish your goal.
Access Policies > Default Network Access > Authorization > Customize > Move "AD1:External Groups" from Available to selected section > ok
Note: Don't forget to call RSA-AD in identity under default network access.
4. test the authentication and report back if needed.
Regards,
Jatin
~Jatin