Hello,
May be the below threads and Notes will give you some helpful information to you
2121902 - UAM: LDAP user assignments are not visible in GRAC_IDM_USER_ASIGNMT_SERVICES webservice
1618524 - GRC 10.0 Access Control Inbound Webservices
activating webservices in GRC 10
http://scn.sap.com/thread/3337756
Regards
Baithi