answering this question need more space than what we have here.
but the answer for the terminating question, if your network is windows based and the administrator is fluent with windows services, you should use both. as each of these servers have different services, like AD (Active Directory) give directory services, and SMS (System Management Service) gives you the ability to monitor your computers in the network.
AD gives services like authentication, resource grouping, and managing their resources in the network for predefined users, or define the network usage policy.
SMS, on the otherhand and with cooperation with AD, may trace the OS (Operating System) update history of the windows, monitoring the network investement, inventory tracing, beside many others ability ones may point.
AD is the essential service needed for central managing of a windows based, or any LDAP compliant networks.
SMS is an addin for serious network managers that need to know and monitor the exact state of each workstation or server, i.e. network investement.
hope this works for you.
best regards,
k.zonouzi ahmad