What Cisco platform can be used in the data center if ACI is not being used to simplify tenant and overlay management?

The most appropriate choice for simplifying tenant and overlay management in a Cisco data center environment, when ACI (Application Centric Infrastructure) is not employed, is VTS (Virtual Traffic Selector). VTS is designed to facilitate traffic visibility and management within a virtualized data center by efficiently managing and monitoring traffic across different tenants and overlays.

VTS can handle complex network traffic flows and provide insights into virtual network infrastructures. It streamlines the process of managing overlay networks, making it easier for administrators to operate and maintain multiple tenancies within a data center without the need for ACI's full framework. Utilizing VTS allows organizations to leverage existing network resources while maintaining a clear overview of network traffic and virtual workloads, which is essential for effective management and operational efficiency.

The other options serve different purposes in the Cisco ecosystem. For example, NSO (Network Services Orchestrator) focuses on network automation and orchestration rather than explicitly on tenant and overlay management. UCS-D (Unified Computing System Director) is aimed at managing compute resources and orchestration in the UCS environment without the same specialization for overlays. WAE (Wide Area Application Services) is primarily concerned with application performance in WAN environments, not specifically with tenant management in the data center context.