Create local accounts for VMware ESXi via PowerCLI is older than 5.5 but maybe it still works.
Did you connect directly to your ESXi host or are you looking for the Local Users & Groups tab when connecting to vCenter? You won't find it there, you have to connect directly to the host.
edit: Your screenshot shows you're connected to vCenter, not directly to the ESXi host. The KB article clearly states that you have to
log in to the host using the vSphere Client
and not the vCenter.
I'm afraid we're talking at cross-purposes here. So let's start again!
1) The KB article you mentioned is about creating ESX(i) local accounts which you can use to log in directly to the ESX(i) host. You cannot use these accounts to grant access when connecting to vCenter. vCenter doesn't know about these accounts as they are local to the hosts. And, yes, you will have to create these accounts on all ESX(i) hosts; remember: They're local to the hosts. However, I don't think your users connect to the hosts directly. In that case http://kb.vmware.com/kb/1027647 won't help you.
2) If you're running vCenter on Windows you can create accounts in the Windows OS and grant them access in vCenter. To the best of my knowledge this is the only option if your vCenter version is < 5.0.
3) I don't know what vCenter version you're running. You said something about a 5.5 cluster; since you're screenshot shows that your host is running ESXi 4.1.0 you maybe run vCenter 5.5...? In that case, you can add vCenter Single Sign-On Users and grant them access.