When you enable the ESXi Shell or SSH on a particular host in a vSphere cluster, a warning will appear on a ESX host:
This is normal behaviour, but you can turn off these warnings for each of the hosts.
Note that prior to vSphere 4.1 Update 2, it is not possible to suppress the warnings.
vim-cmd hostsvc/advopt/update UserVars.SuppressShellWarning long 1
Follow the steps above, depending on the method you'll use. Instead of setting the value to 1, setting the value to 0 will re-enable the warning for the particular ESX host.