vSphere 5.1 added support for SNMPv3, which provides many improvements over SNMPv2. These include added security, with SNMP authentication, and added privacy, with SSL encryption. SNMPv3 also provides additional configuration capabilities through SNMP Set. Also in vSphere 5.1, the SNMP agent has been unbundled from the VMkernel and now runs as an independent agent on the host. This makes it easier to incorporate SNMP updates and patches because they are no longer tied to the vSphere kernel.
ESXis hardware management is based on CIM (with standard or vendor specific CIM providers) and integrated SNMP agents (hosts and vCenter).

vSphere 5 introduced a new, unified CLI, which is using a consistent look and feel for local and remote management + improved syntax.
The esxcli command is available locally on each VMware ESXi host via the ESXi shell, as part of the optional vCLI package that can be installed on any supported Windows or Linux server, or through the vSphere Management Assistant (vMA)
vMA is a Linux-based virtual machine that is pre-installed with a command-line interface and select third-party agents needed to manage your vSphere infrastructure. Administrators and developers can use vMA to run scripts and agents to manage vSphere 5.5, vSphere 5.1 and later, vSphere 5.0 and later systems. vMA includes the vSphere SDK for Perl and the vSphere Command-Line Interface (vSphere CLI).