Please summarize the difference between enabling SSH on a standalone ESX 5.1 host and connecting vs. using the vSphere CLI as far as what commands are available. Does the vCLI have a fair amount of Builtin commands that are not accessible via SSH access?
The scalable approach is to use vCLI or PowerCLI. Their commands are a superset of the ESXi shell's. I work in an environment with multiple tenants, but lots of vSphere clusters. We still do quite a bit of work at the console or via SSH.
ESXi Shell Access
An ESXi system includes a direct console that allows you to start and stop the system and to perform a limited set of maintenance and troubleshooting tasks. The direct console includes the ESXi Shell. The ESXi Shell includes a set of fully supported ESXCLI commands and a set of commands for troubleshooting and remediation. You must enable access to the ESXi Shell from the direct console of each system. You can enable access to the local ESXi Shell or access to the ESXi Shell with SSH.
ESXi Shell Local Access
The ESXi Shell is disabled by default. You can enable the ESXi Shell for troubleshooting from the direct console. All ESXCLI commands that are available in the ESXi Shell are also included in the vCLI package. Install the vCLI package or deploy the vMA virtual appliance, and run commands
SSH allows you to run commands against a single host, while the vCLI allows you to specify one or more hosts at a time.
It's kind of like vCenter versus vSphere. vCenter is for multiple hosts while vSphere gives details on a single host at a time.
You can use this for your reference (the vCLI docs).