Hi Rajini,
Yes, it does support configuring VIP or Hardware Load-balancer url of AD in User Directories, in this case VIP/LB would be responsible for Loadbalance/failover between the available AD DC's.
However Siteminder has got it's own inbuilt LB/Failover mechanism, if you want to use individual AD DC's, refer the below document link for detailed explanation.
LDAP Load Balancing and Failover - CA Single Sign-On - 12.52 SP1 - CA Technologies Documentation
Thanks
Ashok