VMware vSphere Storage APIs – Data Protection (formerly known as VMware vStorage APIs for Data Protection or VADP) FAQ (1021175)
How to back up ESXi host configuration (2042141) with examples for the vSphere CLI, PowerCLI, and the ESX command line.

Veeam

XSIBackup Standalone backup of VMWare ESXi vSphere 5.X virtual machines to another datastore or differential over network. No agents, self capable, runs directly in the hypervisor host, ESXi 5.1, ESXi 5.5 & ESXi 6.0 compatible, hot backups.

running-system.com - Bug in Changed Block Tracking (CBT) may affect your backups – take care of VMware KB 2090639